The Astrophysical Journal, 767:66 (11pp), 2013 April 10
C 2013.
doi:10.1088/0004-637X/767/1/66
The American Astronomical Society. All rights reserved. Printed in the U.S.A.
INSIGHTS INTO SURFACE HYDROGENATION IN THE INTERSTELLAR MEDIUM:
OBSERVATIONS OF METHANIMINE AND METHYL AMINE IN Sgr B2(N)
D. T. Halfen1 , V. V. Ilyushin2 , and L. M. Ziurys1
1
Departments of Chemistry and Astronomy, Arizona Radio Observatory and Steward Observatory,
University of Arizona, Tucson, AZ 85721, USA; [email protected], [email protected]
2 Institute of Radio Astronomy of the National Academy of Sciences Ukraine, Chervonopraporna 4, 61002 Kharkov, Ukraine
Received 2012 October 1; accepted 2013 February 12; published 2013 March 25
ABSTRACT
Multiple observations of methanimine (CH2 NH) and methyl amine (CH3 NH2 ) have been performed toward
Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio
Observatory. In the frequency range 68–280 GHz, 23 transitions of CH2 NH and 170 lines of CH3 NH2 have been
observed as individual, distinguishable features, although some are partially blended with other lines. For CH2 NH,
the line profiles indicate VLSR = 64.2 ± 1.4 km s−1 and ΔV1/2 = 13.8 ± 2.8 km s−1 , while VLSR = 63.7 ± 1.6 km s−1
and ΔV1/2 = 15.1 ± 3.0 km s−1 for CH3 NH2 , parameters that are very similar to those of other organic species
in Sgr B2(N). From these data, rotational diagrams were constructed for both species. In the case of CH2 NH, a
rotational temperature of Trot = 44 ± 13 K and a column density of Ntot = (9.1 ± 4.4) × 1014 cm−2 were determined
from the analysis. For CH3 NH2 , Trot = 159 ± 30 K and Ntot = (5.0 ± 0.9) × 1015 cm−2 , indicating that this species
is present in much warmer gas than CH2 NH. The fractional abundances for CH2 NH and CH3 NH2 were established
to be f (H2 ) ≈ 3.0 × 10−10 and f (H2 ) ≈ 1.7 × 10−9 , respectively. It has been proposed that CH2 NH is formed
on grains via hydrogenation of HCN; further hydrogenation of CH2 NH on surfaces leads to CH3 NH2 . However,
given the dissimilarity between the rotational temperatures and distributions of CH2 NH and CH3 NH2 in Sgr B2, it
is improbable that these species are closely related synthetically, at least in this source. Both CH2 NH and CH3 NH2
are more likely created by neutral–neutral processes in the gas phase.
Key words: astrochemistry – ISM: molecules – line: identification – methods: laboratory – molecular data
Online-only material: color figure
scheme. The intermediate methanimine (CH2 NH), in contrast,
is a stable molecule, and upon saturation yields the end-product
CH3 NH2 .
Both CH2 NH and CH3 NH2 have been observed as gas-phase
interstellar molecules. CH2 NH was first identified by Godfrey
et al. in 1973 in Sgr B2(OH) and subsequently observed by
Turner (1989) in this source, and by Sutton et al. (1991) toward
Sgr B2(M). Nummelin et al. (1998) also detected this molecule
in Sgr B2(N), (M), and (NW). Jones et al. (2008, 2011) have
additionally mapped the distribution of CH2 NH at 3 mm and
7 mm using the MOPRA telescope, and found that it was
extended from Sgr B2(N) to Sgr B2(S), with an emission
peak near Sgr B2(N). CH2 NH has also been observed in the
molecular clouds L183 (Turner et al. 1999), Orion-KL (Dickens
et al. 1997; White et al. 2003), W51, Ori 3N, G34.3+0.15
(Dickens et al. 1997), and G19.61−0.23 (Qin et al. 2010).
Recently, Tenenbaum et al. (2010) identified this species in
the circumstellar envelope of IRC+10216, as well, and it has
also been observed in the starburst galaxy Arp 220 (Salter et al.
2008). Additionally, there is some indication that CH2 NH is
present in Titan’s atmosphere (Vuitton et al. 2007). CH3 NH2 was
first observed by Kaifu et al. (1974, 1975) toward Sgr B2(OH).
Fourikis et al. (1974) also detected this species in the southern
region of Sgr B2 and Fourikis et al. (1977) later found deuterated
methyl amine (CH3 NHD) at that position, as well. Later surveys
conducted by Turner (1989) toward Sgr B2(OH) and Nummelin
et al. (1998) in Sgr B2(N) also found spectral lines of CH3 NH2 .
One interest in both CH2 NH and CH3 NH2 is that they are
thought to be potential interstellar precursors to the amino acid
glycine, NH2 CH2 COOH (Godfrey et al. 1973; Fourikis et al.
1974; Aylward & Bofinger 2001; Bossa et al. 2009; Lee et al.
2009; Theulé et al. 2011; Danger et al. 2011). For example, the
reaction of CH3 NH2 with CO2 in water ice has been shown to
1. INTRODUCTION
Ion–molecule reactions are the dominant gas-phase processes
in the interstellar medium (ISM; Herbst & Klemperer 1973;
Woodall et al. 2007). Synthetic schemes in chemical models
including these reactions have been able to reproduce observed
abundances of many species to within a factor of five (Millar
et al. 1997). However, the abundances of certain molecules,
such as methanol (CH3 OH), have proven harder to replicate
with purely gas-phase reactions (Woodall et al. 2007). As a
consequence, gas-grain models have been developed where
the surfaces of interstellar grains are the sites of chemical
reactions (Tielens & Hagen 1982; Tielens & Charnley 1997;
Garrod et al. 2007). Hydrogenation reactions are predicted to
dominate the chemistry on grains (Tielens & Charnley 1997;
Theulé et al. 2011), as H atoms are mobile on these surfaces
at ∼10–20 K (Tielens & Hagen 1982; Fuchs et al. 2009). In
fact, it is postulated that methanol is predominantly produced
on grains via hydrogenation of CO, through a series of steps that
proceed through HCO, H2 CO, and CH2 OH (Garrod et al. 2007).
This mechanism has been proven experimentally to efficiently
produce methanol in CO ices (e.g., Fuchs et al. 2009). In the
experiment, however, H2 CO was the only intermediate observed
on the ice, while the radical species HCO and CH2 OH were not
detected.
Another series of hydrogenation reactions that could occur on
grain surfaces produces methyl amine (CH3 NH2 ). This process
begins with HCN and proceeds as follows (Theulé et al. 2011):
H
H
H
H
HCN −−→ CH2 N −−→ CH2 NH −−→ CH2 NH2 −−→ CH3 NH2 .
(1)
CH2 N and CH2 NH2 are radical species (Yamamoto & Saito
1992) and are expected to be short-lived intermediates in this
1
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
yield NH2 CH2 COOH after UV irradiation (Bossa et al. 2009;
Lee et al. 2009). In addition, Godfrey et al. (1973) suggested
that CH2 NH could react with HCOOH to form NH2 CH2 COOH.
However, NH2 CH2 COOH has not been securely identified in the
ISM (Snyder et al. 2005).
We have conducted a spectral survey of Sgr B2(N) across the
complete 1, 2, and 3 mm atmospheric windows (D. T. Halfen
et al., in preparation). Multiple favorable transitions of both
CH2 NH and CH3 NH2 were detected in the course of this survey,
prompting further study of their chemical formation routes. Here
we present our measurements of both molecules, the analysis of
the spectra, and abundance determinations, as well as discuss the
implications of these observations for hydrogenation reactions
in the ISM, in particular the scheme given in Equation (1).
Radio Observatory (ARO) 12 m telescope on Kitt Peak and the
Submillimeter Telescope (SMT) on Mount Graham.3
At the 12 m, the receivers employed were dual-polarization,
SIS mixers covering the 3 and 2 mm bands (68–116 and
130–172 GHz). The single-sideband mixers were tuned with
rejection of the image sideband of typically 18 dB. Data were
also obtained with a new dual-channel receiver using ALMA
Band 3 (83–116 GHz) sideband-separating (SBS) mixers. With
these devices, the image rejection was usually 16 dB, attained
within the mixer architecture. The temperature scale was determined by the chopper wheel method, corrected for forward
spillover losses, and is given as TR ∗ . The radiation temperature TR , assuming the source fills only the main beam, is TR =
TR ∗ /ηc , where ηc is the main beam efficiency corrected for forward spillover losses. The spectrometer backend utilized for the
measurements was an autocorrelator (MAC) with either 390 kHz
or 781 kHz resolution, and a bandwidth of 600 MHz channel−1 .
The spectra were smoothed using a cubic spline routine to a
1 MHz resolution.
At the SMT, observations in the frequency range
210–280 GHz (1 mm) were taken with a dual-polarization receiver, which uses ALMA Band 6 SBS mixers with rejection of
at least 16 dB of the image sideband. The temperature scale was
determined by the chopper wheel method, and is given as TA ∗ .
The radiation temperature TR is TR = TA ∗ /ηb , where ηb is the
main beam efficiency. A 2048 channel filter bank with 1 MHz
resolution was utilized as the spectrometer backend, running in
parallel mode (2 × 1024).
The beam size ranged from 87 to 37 at the 12 m and 36
to 23 at the SMT; see Table 1. All observations were conducted toward Sgr B2(N) (α = 17h 44m 09.5s ; δ = −28o 21 20 ;
B1950.0, or α = 17h 47m 19.2s ; δ = −28o 22 22 ; J2000.0: NED
http://ned.ipac.caltech.edu/forms/calculator.html) in positionswitching mode with a +30 OFF position in azimuth. A
10–20 MHz local oscillator shift and direct observation of the
image sideband were employed to identify any image contamination. The pointing accuracy is estimated to be ±5 –10 at
the 12 m and ±1 –2 at the SMT. The telescope pointing was
determined by observations of planets and continuum sources,
such as 1921–293.
2. SPECTROSCOPY OF METHANIMINE
AND METHYL AMINE
Methanimine (CH2 NH) is a planar asymmetric top, and the
simplest molecule with a carbon–nitrogen double bond. The
spectrum consists of both a- and b-type transitions because of
large a and b dipole moments of μa = 1.340 D and μb = 1.446 D
(Allegrini et al. 1979). The rotational spectrum of this molecule
was first recorded by Johnson & Lovas (1972), who measured
transitions in the 60–123 GHz range, including 14 N hyperfine
splittings. Dore et al. (2010, 2012) extended these measurements
up to 629 GHz, and observed transitions involving ΔJ = 0, ±1,
for energy levels up to J = 36 and Ka = 9.
Methyl amine (CH3 NH2 ) is an asymmetric top molecule with
two large-amplitude motions: a methyl group torsion and an
inversion of the amine hydrogens. As a result, the symmetry of
the molecule is characterized by the G12 permutation–inversion
group (Ohashi & Hougen 1987). The spectrum of CH3 NH2 has
been investigated since 1947 (Hershberger & Turkevich 1947),
with multiple studies performed in the 1950s (e.g., Kivelson &
Lide 1957; Nishikawa 1957) and 1970s (e.g., Takagi & Kojima
1973). Various approaches have been used to assign and fit the
data, which give a range for the barrier to inversion from 1686
to 2081 cm−1 (Ohashi et al. 1987). The most successful method
was developed by Ohashi & Hougen (1987), based on a grouptheoretical formalism, where the spectra are assigned using
an inversion–internal-rotation–rotation-Hamiltonian (Ilyushin
et al. 2005). In this scheme, the allowed transitions are labeled
with the A1 , A2 , B1 , B2 , E1 ± 1 , and E2 ± 1 torsion-inversionrotation irreducible representations Γ (Ilyushin & Lovas 2007),
and the selection rules are Γ = A1 ↔ A2 , B1 ↔ B2 , E1±1 ↔
E1±1 , and E2±1 ↔ E2±1 . The dipole moments for CH3 NH2
are μa = −0.307 D and μc = 1.258 D (Lide 1957; Takagi &
Kojima 1971). The symmetry levels have nuclear spin-statistical
weights of 1 for the A1 , A2 , and E2 states and 3 for the B1 ,
B2 , and E1 components. Many experimental studies have been
conducted of CH3 NH2 , as summarized by Ohashi et al. (1987),
and more recently by Ilyushin et al. (2005), such that the data
now encompass the 3–461 GHz range and from 40 to 350 cm−1
in the far-infrared region. The microwave studies encompass
transitions for J = 0–30 and Ka = 0–9 for all symmetry
components.
4. RESULTS
Figure 1 gives a pictorial representation of all current observations of CH2 NH and CH3 NH2 towards the Sgr B2 region, centered at Sgr B2(M), α = 17h 44m 11s ; δ = −28◦ 22 00 ; B1950.0
or α = 17h 47m 20.8s ; δ = −28o 23 02 ; J2000.0. The major hot
(N, M, and S) and cold (OH, NW, and 2N) cores in this area
are indicated: i.e., Sgr B2(N), (M), (OH), (S), (NW), and (2N).
The positions with corresponding beam sizes, where CH2 NH
and CH3 NH2 have been identified, are indicated by solid and
dashed circles, respectively. The measurements conducted in
this work, centered on Sgr B2(N), are shown with darker traces.
The Nummelin et al. (1998), Sutton et al. (1991), Kaifu et al.
(1974, 1975), Turner (1989), and Fourikis et al. (1974, 1977)
detections are indicated on the figure with an N, S, K, T, and
F, while this work is labeled with an H. Godfrey et al. (1973)
did not report observing coordinates, but it is assumed that they
centered their 3.8 beam on Sgr B2(OH). As the figure shows,
multiple observations of CH3 NH2 have been performed across
3. OBSERVATIONS
The spectra of CH2 NH and CH3 NH2 observed here are part
of a complete spectral-line survey of the 1, 2, and 3 mm
windows toward Sgr B2(N). The data were recorded during
the period 2002 September to 2012 June using the Arizona
3
The 12 m telescope and the SMT are operated by the Arizona Radio
Observatory (ARO), Steward Observatory, University of Arizona, with partial
support from the NSF University Radio Observatories (URO) program.
2
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Table 1
Observed Rotational Transitions of Methanimine in Sgr B2(N)
J
Ka Kc ↔
J
Ka Kc Frequency
(MHz)
θb
( )
5
7
4
6
2
4
7
1
5
4
1
6
4
7
6
4
4
4
4
4
3
4
8
1
2
0
1
1
2
1
1
2
2
1
1
1
1
0
0
2
3
3
2
2
1
1
4
5
4
5
1
3
6
0
3
2
1
5
4
6
6
4
3
2
1
2
1
3
7
→
→
→
→
→
→
→
←
→
→
←
→
→
→
→
→
→
→
→
→
→
→
→
5
8
3
6
1
5
7
1
6
5
0
6
3
7
5
3
3
3
3
3
4
3
8
1
1
1
1
1
1
1
0
1
1
0
0
1
0
1
0
2
3
3
2
1
1
0
5
8
3
6
0
4
7
1
6
5
0
6
3
7
5
3
2
1
0
1
4
2
8
79281.24b
95306.84b
105794.06b
110897.74b
133272.09b
133734.90b
147660.59
166851.76b
170015.92
214926.47
225554.61
226548.73
245125.87
250161.78
251421.27
254685.14
255840.31
256165.29
256176.84
257112.63
263986.09
266270.02
278642.61
79
66
59
57
47
47
43
38
37
35
33
33
31
30
30
30
29
29
29
29
29
28
27
ηc or ηb
0.92
0.89
0.87
0.86
0.80
0.80
0.76
0.70
0.69
0.76
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
a
TR ∗ or TA ∗
(K)
a
0.032 ± 0.002
0.036 ± 0.003
0.619 ± 0.002
0.054 ± 0.002
0.762 ± 0.003
0.121 ± 0.003
0.038 ± 0.007
−0.424 ± 0.005
0.242 ± 0.007
0.189 ± 0.005
−0.659 ± 0.005
0.620 ± 0.004
1.150 ± 0.006
0.678 ± 0.005
0.793 ± 0.005
1.715 ± 0.006
0.650 ± 0.004
0.550 ± 0.004
0.384 ± 0.004
0.587 ± 0.005
0.211 ± 0.005
1.522 ± 0.004
0.434 ± 0.005
ΔV1/2
(km s−1 )
VLSR
(km s−1 )
Eu
(K)
μ2 S
(D2 )
15.0 ± 3.8
12.6 ± 3.1
17.0 ± 2.8
16.2 ± 2.7
18.0 ± 2.2
13.2 ± 2.2
8.1 ± 2.0
66.5 ± 3.8
61.1 ± 3.1
61.3 ± 2.8
64.2 ± 2.7
65.2 ± 2.2
65.3 ± 2.2
63.1 ± 2.0
65.2 ± 1.8
63.6 ± 1.8
65.3 ± 1.4
64.1 ± 1.3
64.3 ± 1.3
65.3 ± 1.2
65.9 ± 1.2
65.3 ± 1.2
62.8 ± 1.2
63.9 ± 1.2
63.9 ± 1.2
64.2 ± 1.2
64.0 ± 1.2
64.0 ± 1.1
65.1 ± 1.1
64.5 ± 1.1
55.84
118.23
30.64
74.99
17.49
62.26
97.29
11.09
77.82
62.35
10.83
74.99
37.33
97.29
64.11
30.64
62.26
101.69
101.69
62.35
50.01
39.87
122.75
1.98
5.39
10.54
1.68
8.07
4.21
1.46
9.40
4.21
3.27
6.27
34.25
20.17
37.04
19.14
21.50
16.14
9.42
9.42
16.14
2.17
20.17
38.96
10.6 ± 1.8
11.2 ± 1.4
16.0 ± 1.3
13.5 ± 1.2
12.0 ± 1.2
16.7 ± 1.2
16.4 ± 1.2
11.7 ± 1.2
11.7 ± 1.2
11.7 ± 1.2
18.6 ± 1.2
13.6 ± 1.1
14.6 ± 1.1
10.8 ± 1.1
Comments
Partially blended
Blended with HC13 CCN
Blended with CH3 OCH3
Absorption feature
Partially blended
Absorption feature
Partially blended
Partially blended
Partially blended
Partially blended
Notes.
a T ∗ and η pertain to frequencies <172 GHz (12 m data), and T ∗ and η apply to frequencies >210 GHz (SMT observations).
R
c
A
b
b Transition frequency measured in laboratory (e.g., Dore et al. 2010); higher frequency lines (ν > 329 GHz) recorded by Dore et al. (2012).
the Sgr B2 region. These measurements indicate that this species
is present throughout the complex, from the N position to at least
1 arcmin south of Sgr B2(S), and not confined to just one hot
core, such as Sgr B2(N). Past detections of CH2 NH at the N,
NW, M, and OH positions indicate that the distribution of this
species is also extended across the Sgr B2 cloud (see Figure 1).
Table 1 summarizes the data for CH2 NH. The table lists
the quantum numbers, rest frequencies, telescope parameters,
upper state energy (Eu ), and the product of the square of the
dipole moment μ with the line strength (μ2 S) for this molecule.
Twenty-three out of 109 measured (or predicted) rotational
transitions (μ2 S > 1.2 D2 and Eu > 10.8 K) in the 1, 2, and
3 mm survey range (68–116, 130–172, and 210–280 GHz)
were detected as individual, distinguishable features, although
six are partially blended. The other 86 lines were completely
contaminated by stronger lines in the spectrum, which is a
common problem in Sgr B2(N), given the high line density
and spectral complexity. All observed lines are consistent with
their intrinsic line strength and energy above ground state, with
no “missing” transitions, i.e., emission is present at all favorable
transitions. Two lines were seen in absorption, as indicated by
the negative TR ∗ value. As shown in Table 2, the data set for
CH2 NH has an almost equal number of a- and b-type transitions
covering J = 1–8 and Ka = 0–3, and arising from energy levels
with Eu = 11–123 K (7–85 cm−1 ).
Figure 2 shows an energy level diagram for CH2 NH. All
observed transitions are indicated with arrows; absorption
(JK a ,K c = 110 ← 101 and 111 ← 000 ) and emission features
are differentiated by the arrow directions. Also shown in the
figure are two transitions (JK a ,K c = 514 → 413 and 313 ← 202 )
observed by Sutton et al. (1991) toward Sgr B2(M). Two additional lines (JK a ,K c = 111 ← 202 and 303 → 212 ) are displayed
in the diagram, as well. These features were observed with the
NRAO GBT telescope toward Sgr B2(N) as part of the PRIMOS survey, with beam size of ∼22 (Remijan et al. 2008).
Ten of the transitions at 1 mm had been previously reported by
Nummelin et al. (1998), as well as a line at 105.8 GHz, observed by Jones et al. (2011). The JK a ,K c = 111 ← 202 line from
Remijan et al. (2008) and 313 ← 202 transition from Sutton et al.
(1991) were also seen in absorption. As the diagram illustrates,
all transitions of CH2 NH observed to date toward Sgr B2(N)
and (M) with lower-state energies below El ∼ 10 K have been
measured in absorption, while those with El > 10 K were detected in emission. This result implies a two-source geometry
with cooler, foreground gas and warmer, perhaps denser, material behind it. From the energies of the absorbing line source,
the foreground gas has TK < 10 K.
Representative spectra of CH2 NH are shown in Figure 3.
The spectral resolution of the data is 1 MHz, and the transition
and rest frequencies are given on each spectrum. The CH2 NH
features are indicated by arrows near VLSR = 62 km s−1 . The
JK a ,K c = 423 → 514 , 414 → 313 , and 413 → 312 transitions appear
to be single, clean emission lines. In contrast, the JK a ,K c =
111 ← 000 transition appears in absorption with an apparent
second velocity component from gas with an LSR velocity near
80 km s−1 .
The data obtained for CH3 NH2 are summarized in Table 2.
Here the quantum numbers, rest frequencies, telescope parameters, upper state energy (Eu ), and μ2 S are given. Out of 580
measured (or predicted) transitions (μ2 S > 0.02 D2 and Eu >
6.1 K) in the current frequency range (68–116, 130–172, and
210–280 GHz), 170 were clearly identified in this data set,
including both a- and c-type transitions, and are reported in
the table. The remaining 410 CH3 NH2 transitions are completely blended with or masked by other spectral features, some
which have quite strong emission. All lines were checked for
3
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Table 2
Observed Rotational Transitions of Methyl Amine in Sgr B2(N)
J
Ka Γ
→
J
Ka Γ
Frequency
(MHz)
θb
( )
7
6
9
6
5
5
4
8
7
4
3
3
7
7
6
11
4
5
11
11
6
4
11
3
2
2
2
8
6
11
4
4
6
4
27
2
8
26
4
2
1
3
3
12
12
3
3
3
3
3
5
9
16
8
22
5
5
5
12
5
9
16
21
21
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
2
2
3
1
2
1
1
1
1
1
3
2
0
0
3
0
2
2
1
2
0
2
1
1
1
2
2
0
0
0
0
1
0
1
3
1
2
0
0
3
2
3
1
3
2
2
1
E1−1
B2
A1
E1−1
B1
E1−1
B2
A2
A2
E1−1
B1
E1−1
A1
E1+1
A2
B1
E2+1
A1
A1
E1−1
E1+1
A2
B2
A1
E1−1
E2−1
A2
A2
B2
E1+1
E2+1
B1
E2−1
E1+1
E2+1
E2+1
E1−1
E1−1
E2+1
A1
E2−1
B1
A1
E2−1
B1
B2
E2+1
E1+1
A2
E1+1
E1+1
E1−1
E1+1
E1+1
E1−1
B2
E2+1
B2
E1+1
E2−1
E1−1
E2+1
E2+1
A1
E2−1
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
7
6
9
6
5
5
4
8
6
4
3
3
7
6
6
10
4
5
10
10
7
4
10
3
1
1
2
7
7
10
3
3
7
3
27
3
7
26
3
3
0
2
2
11
11
2
2
2
2
2
4
8
15
7
22
4
4
6
11
6
8
15
21
21
1
0
0
0
0
0
0
0
0
2
0
0
0
0
2
0
3
0
0
3
3
2
0
3
0
1
1
0
2
2
3
1
1
2
1
1
1
2
1
1
1
0
1
1
3
3
0
0
0
0
1
1
2
4
2
1
1
1
2
3
2
2
4
1
1
0
E1+1
B1
A2
E1−1
B2
E1+1
B1
A1
A1
E1+1
B2
E1+1
A2
E1+1
A1
B2
E2+1
A2
A2
E1+1
E1+1
A1
B1
A2
E1−1
E2−1
A1
A1
B1
E1+1
E2+1
B2
E2−1
E1−1
E2+1
E2+1
E1−1
E1+1
E2−1
A2
E2+1
B2
A2
E2+1
B2
B1
E2+1
E1+1
A1
E1+1
E1+1
E1+1
E1+1
E1−1
E1+1
B1
E2+1
B1
E1+1
E2−1
E1−1
E2+1
E2+1
A2
E2+1
69903.704b
70594.237b
72309.083b
72586.983b
73044.473b
74901.933b
75134.858b
75648.042b
76398.848b
76782.307b
76838.932b
78146.174b
78732.155b
79402.446b
81521.078b
82164.188b
83752.950b
83978.941b
84043.256
84391.631b
84454.892b
86074.729b
87049.054b
87782.494b
88387.971b
88547.665b
89081.463b
92981.820b
94052.694b
94420.198b
94466.155b
95145.307b
95746.970b
99127.285b
100907.737b
101236.885
103668.361b
106365.824b
107461.887b
109959.713b
114658.597b
131685.367b
131685.766b
132335.126b
132728.522b
132981.939b
132982.388b
132983.798b
132984.734b
133810.676b
134631.684b
134845.631b
135195.126b
135645.829b
137521.807b
137583.292b
137774.487b
137797.088b
139727.165b
140254.570b
143691.412b
145726.089b
147898.694b
152047.614
158867.794
90
89
87
87
86
84
84
83
82
82
82
80
80
79
77
77
75
75
75
74
74
73
72
72
71
71
71
68
67
67
67
66
66
63
62
62
61
59
59
57
55
48
48
48
47
47
47
47
47
47
47
47
47
46
46
46
46
46
45
45
44
43
43
41
40
ηc or ηb
0.94
0.94
0.94
0.94
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.92
0.92
0.92
0.92
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.90
0.90
0.89
0.89
0.89
0.89
0.89
0.88
0.88
0.88
0.87
0.87
0.86
0.86
0.85
0.80
0.80
0.80
0.80
0.80
0.80
0.80
0.80
0.80
0.79
0.79
0.79
0.79
0.79
0.79
0.79
0.79
0.78
0.78
0.77
0.76
0.76
0.75
0.73
a
TR ∗ or TA ∗
(K)
a
0.097 ± 0.002
0.109 ± 0.002
0.044 ± 0.003
0.101 ± 0.003
0.148 ± 0.003
0.128 ± 0.003
0.126 ± 0.003
0.044 ± 0.003
0.019 ± 0.002
0.048 ± 0.002
0.135 ± 0.002
0.048 ± 0.003
0.034 ± 0.003
0.023 ± 0.003
0.062 ± 0.002
0.023 ± 0.002
0.016 ± 0.003
0.049 ± 0.003
0.026 ± 0.002
0.038 ± 0.002
0.112 ± 0.002
0.054 ± 0.002
0.020 ± 0.003
0.055 ± 0.002
0.034 ± 0.002
0.015 ± 0.003
0.040 ± 0.002
0.031 ± 0.002
0.012 ± 0.003
0.101 ± 0.003
0.067 ± 0.003
0.259 ± 0.002
0.071 ± 0.002
0.041 ± 0.003
0.019 ± 0.003
0.039 ± 0.003
0.027 ± 0.002
0.023 ± 0.003
0.029 ± 0.003
0.091 ± 0.002
0.026 ± 0.004
0.059 ± 0.005
0.059 ± 0.005
0.093 ± 0.004
0.161 ± 0.004
0.282 ± 0.003
0.282 ± 0.003
0.331 ± 0.003
0.331 ± 0.003
0.066 ± 0.003
0.397 ± 0.006
0.068 ± 0.006
0.030 ± 0.008
0.024 ± 0.005
0.045 ± 0.003
0.291 ± 0.003
0.067 ± 0.003
0.056 ± 0.003
0.065 ± 0.002
0.034 ± 0.003
0.086 ± 0.005
0.054 ± 0.005
0.055 ± 0.005
0.076 ± 0.004
0.013 ± 0.003
4
ΔV1/2
(km s−1 )
VLSR
(km s−1 )
Eu
(K)
μ2 S
(D2 )
17.2 ± 4.3
21.2 ± 4.2
20.7 ± 4.1
20.7 ± 4.1
20.5 ± 4.1
20.0 ± 4.0
20.0 ± 4.0
19.8 ± 4.0
15.7 ± 3.9
15.6 ± 3.9
19.5 ± 3.9
19.2 ± 3.8
15.2 ± 3.8
18.9 ± 3.8
18.4 ± 3.7
14.6 ± 3.6
17.9 ± 3.6
14.3 ± 3.6
17.8 ± 3.6
14.2 ± 3.6
17.8 ± 3.5
17.4 ± 3.5
13.8 ± 3.4
17.1 ± 3.4
17.0 ± 3.4
20.3 ± 3.4
21.5 ± 3.4
19.3 ± 3.2
15.9 ± 3.2
19.1 ± 3.2
22.2 ± 3.2
22.1 ± 3.2
18.8 ± 3.1
18.1 ± 3.0
17.8 ± 3.0
17.8 ± 3.0
17.4 ± 2.9
14.1 ± 2.8
16.8 ± 2.8
16.4 ± 2.7
16.1 ± 2.7
16.9 ± 2.3
16.9 ± 2.3
13.6 ± 2.3
17.0 ± 2.3
18.0 ± 2.3
18.0 ± 2.3
18.2 ± 2.3
18.2 ± 2.3
17.9 ± 2.2
17.8 ± 2.2
13.3 ± 2.2
13.3 ± 2.2
13.3 ± 2.2
15.3 ± 2.2
17.4 ± 2.2
17.4 ± 2.2
15.2 ± 2.2
15.0 ± 2.1
15.0 ± 2.1
20.9 ± 2.1
14.4 ± 2.1
16.2 ± 2.0
15.8 ± 2.0
15.1 ± 1.9
65.3 ± 4.3
65.5 ± 4.2
62.1 ± 4.1
64.0 ± 4.1
65.1 ± 4.1
65.2 ± 4.0
64.7 ± 4.0
62.9 ± 4.0
64.4 ± 3.9
62.3 ± 3.9
64.4 ± 3.9
61.9 ± 3.8
62.8 ± 3.8
66.6 ± 3.8
64.3 ± 3.7
62.9 ± 3.6
60.3 ± 3.6
65.5 ± 3.6
62.7 ± 3.6
66.7 ± 3.6
65.6 ± 3.5
60.3 ± 3.5
64.3 ± 3.4
66.1 ± 3.4
65.7 ± 3.4
60.3 ± 3.4
62.8 ± 3.4
64.7 ± 3.2
62.1 ± 3.2
62.5 ± 3.2
66.6 ± 3.2
64.0 ± 3.2
65.4 ± 3.1
64.4 ± 3.0
60.9 ± 3.0
61.8 ± 3.0
61.6 ± 2.9
64.6 ± 2.8
62.8 ± 2.8
65.0 ± 2.7
62.9 ± 2.7
66.1 ± 2.3
66.1 ± 2.3
62.0 ± 2.3
63.5 ± 2.3
62.7 ± 2.3
62.7 ± 2.3
63.0 ± 2.3
63.0 ± 2.3
61.2 ± 2.2
64.6 ± 2.2
64.0 ± 2.2
62.3 ± 2.2
63.8 ± 2.2
60.0 ± 2.2
64.7 ± 2.2
65.1 ± 2.2
62.9 ± 2.2
65.7 ± 2.1
64.0 ± 2.1
63.5 ± 2.1
60.6 ± 2.1
61.9 ± 2.0
63.1 ± 2.0
61.6 ± 1.9
63.36
48.37
99.16
48.60
35.73
35.95
25.19
80.21
64.53
25.41
16.76
16.96
63.35
64.56
48.60
156.65
25.89
35.96
156.59
156.16
79.71
25.42
156.88
16.99
10.61
10.34
10.67
80.21
80.31
156.64
21.87
21.58
80.12
21.72
818.26
22.19
80.22
761.08
21.87
22.52
6.09
16.76
16.99
182.17
182.50
13.07
13.36
13.21
12.77
17.31
32.36
99.18
324.56
81.75
553.41
32.22
32.51
67.54
182.24
67.35
99.18
324.85
506.78
507.07
10.34
12.61
10.83
16.74
10.66
9.02
8.74
7.29
14.67
1.84
6.82
5.61
4.84
12.70
1.15
10.82
2.60
1.48
9.02
2.60
0.18
1.13
7.29
2.62
5.61
0.14
0.14
3.98
1.93
1.13
2.43
1.60
2.28
1.06
0.31
36.24
0.25
1.23
33.82
0.68
0.27
0.73
0.25
0.25
1.10
3.01
0.28
0.28
0.28
0.28
0.25
2.79
0.78
3.90
0.88
25.13
2.99
2.38
0.79
2.66
0.77
1.48
3.75
23.33
23.33
0.93
Comments
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Blended transitions
Blended transitions
Blended transitions
Blended transitions
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Table 2
(Continued)
J
Ka Γ
→
J
Ka Γ
Frequency
(MHz)
θb
( )
10
19
18
2
2
13
3
10
11
11
14
10
12
3
9
11
11
11
3
12
10
8
5
5
5
7
9
5
5
5
11
7
10
11
10
5
5
5
9
6
14
9
3
7
10
8
4
7
8
9
5
7
2
5
6
4
7
4
3
5
6
3
6
2
5
1
2
2
1
1
2
1
2
2
1
2
1
2
1
2
1
2
2
3
2
1
2
1
1
1
0
2
2
2
2
1
2
1
2
1
1
1
1
2
2
2
2
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
B2
A1
E1−1
E1−1
B1
E1+1
E1−1
E1−1
E2+1
E1−1
B2
B1
E1+1
B2
E1−1
E2−1
A1
E1+1
E1+1
B2
A1
E1−1
B1
A1
E1−1
B2
E2+1
B1
A1
B2
E1−1
E1−1
E1+1
B1
E2+1
E1+1
A2
B2
E1+1
E1−1
B1
A1
A2
E2+1
B2
E1+1
E1−1
E2−1
A2
B1
E2+1
A1
E2+1
E1+1
A2
E1+1
B1
E1−1
E1+1
E1−1
B2
A1
E1−1
A2
B1
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
9
19
18
1
1
13
2
10
11
10
13
9
12
2
9
10
11
11
4
12
9
8
4
4
4
6
9
4
4
4
10
7
9
11
9
4
4
4
9
6
13
9
2
7
10
8
4
7
8
9
5
7
2
5
6
4
7
4
3
5
6
3
6
2
5
2
1
1
0
0
1
0
1
1
2
3
2
1
0
1
2
1
1
2
1
2
1
1
1
1
1
1
2
2
2
2
1
2
1
2
1
1
1
1
1
3
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
B1
A2
E1+1
E1+1
B2
E1+1
E1+1
E1+1
E2+1
E1+1
B1
B2
E1+1
B1
E1+1
E2+1
A2
E1+1
E1+1
B1
A2
E1+1
B2
A2
E1−1
B1
E2+1
B2
A2
B1
E1−1
E1+1
E1+1
B2
E2−1
E1+1
A1
B1
E1+1
E1+1
B2
A2
A1
E2+1
B1
E1+1
E1+1
E2+1
A1
B2
E2+1
A2
E2+1
E1+1
A1
E1+1
B2
E1−1
E1+1
E1−1
B1
A2
E1−1
A1
B2
167112.266
167174.043
167188.848
167598.269
169447.484b
210909.957
211129.971
211839.029
212338.485
212685.476
213053.137
213184.172
214198.947
215108.726
215670.049
215927.863
217079.373b
217669.997
217670.157
217758.226
219005.088
219151.222
219440.096
219440.497
219650.030
220826.704b
220888.443b
221651.281
221651.982
221791.559b
222050.948
222282.224
222590.740
222846.153b
223325.310
223629.263b
223837.331
223844.565
224682.489
225045.153
225101.833
226034.388b
226045.921
227497.908b
227545.018b
227997.003b
229310.604
229452.729
229908.120b
231844.267b
232003.755b
233368.423b
234657.948b
236159.884b
236408.779b
238067.376b
239209.612b
239427.017b
239446.259b
241501.242
242261.957
242961.361
244151.624
244277.744
244886.856
38
38
38
38
37
36
36
36
36
35
35
35
35
35
35
35
35
35
35
35
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
34
33
33
33
33
33
33
33
33
33
33
32
32
32
32
32
32
32
32
31
31
31
31
31
31
ηc or ηb
0.70
0.70
0.70
0.70
0.69
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.76
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
a
TR ∗ or TA ∗
(K)
a
0.059 ± 0.005
0.029 ± 0.005
0.072 ± 0.005
0.138 ± 0.004
0.148 ± 0.009
0.112 ± 0.004
0.135 ± 0.004
0.201 ± 0.005
0.317 ± 0.005
0.157 ± 0.005
0.201 ± 0.005
0.184 ± 0.005
0.128 ± 0.005
0.574 ± 0.005
0.255 ± 0.005
0.070 ± 0.005
0.238 ± 0.005
0.048 ± 0.004
0.048 ± 0.004
0.177 ± 0.004
0.074 ± 0.005
0.201 ± 0.005
0.173 ± 0.005
0.173 ± 0.005
0.235 ± 0.005
0.354 ± 0.005
0.206 ± 0.005
0.229 ± 0.005
0.229 ± 0.005
0.153 ± 0.005
0.179 ± 0.005
0.120 ± 0.005
0.172 ± 0.005
0.223 ± 0.005
0.220 ± 0.005
0.067 ± 0.004
0.037 ± 0.004
0.095 ± 0.004
0.230 ± 0.004
0.136 ± 0.004
0.306 ± 0.004
0.126 ± 0.005
0.115 ± 0.005
0.135 ± 0.004
0.356 ± 0.003
0.224 ± 0.003
0.200 ± 0.005
0.036 ± 0.005
0.156 ± 0.004
0.935 ± 0.005
0.421 ± 0.005
0.303 ± 0.006
0.134 ± 0.006
0.487 ± 0.005
0.480 ± 0.005
0.311 ± 0.004
0.750 ± 0.004
0.140 ± 0.004
0.114 ± 0.004
0.451 ± 0.004
0.270 ± 0.004
0.161 ± 0.004
0.268 ± 0.005
0.190 ± 0.005
0.388 ± 0.006
5
ΔV1/2
(km s−1 )
VLSR
(km s−1 )
Eu
(K)
μ2 S
(D2 )
12.6 ± 1.8
14.4 ± 1.8
16.1 ± 1.8
15.0 ± 1.8
15.9 ± 1.8
19.9 ± 1.4
17.0 ± 1.4
15.6 ± 1.4
14.4 ± 1.4
16.9 ± 1.4
14.4 ± 1.4
12.7 ± 1.4
14.0 ± 1.4
19.5 ± 1.4
19.4 ± 1.4
11.1 ± 1.4
13.8 ± 1.4
11.0 ± 1.4
11.0 ± 1.4
15.1 ± 1.4
11.0 ± 1.4
13.7 ± 1.4
13.7 ± 1.4
13.7 ± 1.4
16.2 ± 1.4
12.9 ± 1.4
11.2 ± 1.4
14.0 ± 1.4
14.0 ± 1.4
16.2 ± 1.4
19.6 ± 1.4
10.8 ± 1.3
15.1 ± 1.3
12.1 ± 1.3
16.6 ± 1.3
10.6 ± 1.3
10.9 ± 1.3
10.1 ± 1.3
12.1 ± 1.3
10.8 ± 1.3
13.4 ± 1.3
15.1 ± 1.3
16.6 ± 1.3
13.6 ± 1.3
18.3 ± 1.3
13.6 ± 1.3
14.0 ± 1.3
10.5 ± 1.3
10.7 ± 1.3
16.6 ± 1.3
15.9 ± 1.3
13.3 ± 1.3
14.2 ± 1.3
15.0 ± 1.3
15.2 ± 1.3
13.6 ± 1.3
13.8 ± 1.3
12.5 ± 1.3
13.8 ± 1.3
14.7 ± 1.2
11.1 ± 1.2
18.6 ± 1.2
12.7 ± 1.2
13.6 ± 1.2
11.9 ± 1.2
63.4 ± 1.8
64.4 ± 1.8
62.6 ± 1.8
63.0 ± 1.8
60.7 ± 1.8
63.4 ± 1.4
65.8 ± 1.4
63.8 ± 1.4
63.7 ± 1.4
63.5 ± 1.4
64.2 ± 1.4
64.4 ± 1.4
65.0 ± 1.4
63.0 ± 1.4
66.2 ± 1.4
64.3 ± 1.4
61.1 ± 1.4
63.1 ± 1.4
63.1 ± 1.4
63.6 ± 1.4
61.7 ± 1.4
61.7 ± 1.4
65.2 ± 1.4
65.2 ± 1.4
63.9 ± 1.4
65.8 ± 1.4
64.3 ± 1.4
63.8 ± 1.4
63.8 ± 1.4
63.4 ± 1.4
61.0 ± 1.4
64.6 ± 1.3
66.0 ± 1.3
64.6 ± 1.3
63.6 ± 1.3
64.6 ± 1.3
63.2 ± 1.3
61.8 ± 1.3
64.2 ± 1.3
64.9 ± 1.3
60.9 ± 1.3
62.8 ± 1.3
66.4 ± 1.3
63.7 ± 1.3
66.9 ± 1.3
64.4 ± 1.3
63.5 ± 1.3
61.0 ± 1.3
64.8 ± 1.3
60.3 ± 1.3
66.9 ± 1.3
66.9 ± 1.3
63.6 ± 1.3
64.0 ± 1.3
63.9 ± 1.3
65.2 ± 1.3
63.6 ± 1.3
63.4 ± 1.3
64.2 ± 1.3
66.0 ± 1.2
64.1 ± 1.2
62.7 ± 1.2
65.2 ± 1.2
66.9 ± 1.2
63.9 ± 1.2
120.00
420.07
379.39
10.61
10.56
209.98
16.96
132.74
156.30
143.40
239.57
122.32
182.24
17.01
111.44
143.26
156.59
156.64
47.78
182.17
122.54
92.28
35.73
35.96
35.95
59.87
111.62
48.12
48.07
48.14
143.40
75.24
122.57
156.64
122.48
36.63
36.59
36.36
111.88
60.33
240.16
111.92
17.24
75.43
133.25
92.70
36.90
75.52
92.77
111.97
47.75
75.74
22.19
47.97
60.84
37.32
75.79
36.90
28.81
47.55
60.90
28.91
60.33
22.52
48.12
2.57
19.96
18.13
0.64
2.37
1.70
0.44
5.68
9.69
0.75
3.75
3.36
2.22
3.16
4.49
2.55
9.78
2.71
0.20
10.83
3.35
3.52
0.45
0.45
0.45
4.30
7.50
0.40
0.40
0.40
2.11
2.71
2.27
9.77
2.83
0.45
0.45
0.45
3.29
2.02
3.83
7.79
3.16
5.25
8.76
3.32
0.85
0.63
6.84
7.78
3.58
5.92
1.29
2.71
5.02
2.38
5.92
2.30
1.94
2.55
5.02
2.32
2.73
1.32
4.13
Comments
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Blended transitions
Blended transitions
Partially blended
Partially blended
Blended transitions
Blended transitions
Partially blended
Blended transitions
Blended transitions
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Table 2
(Continued)
J
Ka Γ
→
J
Ka Γ
Frequency
(MHz)
θb
( )
12
3
4
7
3
4
8
5
6
6
4
3
4
7
5
7
8
12
11
4
4
8
8
6
4
9
6
11
9
6
6
10
10
4
10
9
11
11
15
11
1
2
2
2
2
2
0
2
2
2
1
2
2
2
2
2
0
1
1
1
1
0
0
1
1
2
2
1
2
1
1
2
2
1
2
2
2
2
2
2
B2
E1+1
B2
E1−1
B1
A1
A1
E2−1
E1+1
E2−1
E1−1
B2
B1
E2−1
B2
A2
E1+1
E1−1
B2
E2+1
B1
B1
E2+1
E2−1
E1+1
E2−1
B1
A2
A2
E1+1
B1
E1+1
E2−1
A1
A1
B2
E1+1
E2−1
E1+1
A2
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
→
11
3
4
7
3
4
7
5
6
6
3
3
4
7
5
7
7
11
10
3
3
7
7
5
3
9
5
10
9
5
5
10
10
3
10
9
11
11
14
11
2
1
1
1
1
1
1
1
1
1
0
1
1
1
1
1
1
2
2
0
0
1
1
1
0
1
2
2
1
1
1
1
1
0
1
1
1
1
3
1
B1
E1−1
B1
E1−1
B2
A2
A2
E2−1
E1−1
E2−1
E1+1
B1
B2
E2−1
B1
A1
E1+1
E1−1
B1
E2+1
B2
B2
E2+1
E2−1
E1+1
E2−1
B2
A1
A1
E1+1
B2
E1−1
E2−1
A2
A2
B1
E1−1
E2−1
E1+1
A1
245202.161
246725.165
247080.140
247362.353
248838.500
250110.220
250702.202
251499.754
252908.786
253768.569
254055.766
254161.468
255997.778
256759.656
258349.241
258857.426
259042.415
260427.074
260963.398b
261024.312
261219.283b
261562.178b
263377.814
263840.124b
264172.179
265064.448b
266202.673b
266775.423b
267838.721
268442.510
268582.407
269659.456
270476.894b
272148.016
273440.209b
273745.927b
275674.606
276793.445
278217.266
279866.780
31
31
31
30
30
30
30
30
30
30
30
30
29
29
29
29
29
29
29
29
29
29
29
29
29
28
28
28
28
28
28
28
28
28
28
28
27
27
27
27
ηc or ηb
TR ∗ or TA ∗
(K)
a
a
0.171 ± 0.006
0.097 ± 0.004
0.672 ± 0.004
0.316 ± 0.004
0.364 ± 0.005
0.136 ± 0.005
0.155 ± 0.005
0.666 ± 0.005
0.205 ± 0.005
0.287 ± 0.005
0.171 ± 0.005
0.140 ± 0.005
0.311 ± 0.004
0.256 ± 0.005
0.404 ± 0.005
0.100 ± 0.006
0.427 ± 0.006
0.334 ± 0.004
0.330 ± 0.005
0.197 ± 0.005
0.458 ± 0.005
0.772 ± 0.005
0.212 ± 0.004
0.233 ± 0.005
0.633 ± 0.005
0.227 ± 0.004
0.155 ± 0.004
0.089 ± 0.004
0.139 ± 0.004
0.237 ± 0.004
0.179 ± 0.005
0.206 ± 0.005
0.117 ± 0.005
0.295 ± 0.005
0.185 ± 0.005
0.539 ± 0.005
0.291 ± 0.005
0.177 ± 0.005
0.407 ± 0.004
0.173 ± 0.005
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
ΔV1/2
(km s−1 )
VLSR
(km s−1 )
Eu
(K)
μ2 S
(D2 )
11.0 ± 1.2
10.0 ± 1.2
15.4 ± 1.2
13.0 ± 1.2
15.2 ± 1.2
11.3 ± 1.2
14.8 ± 1.2
16.6 ± 1.2
19.0 ± 1.2
12.1 ± 1.2
10.6 ± 1.2
10.6 ± 1.2
15.9 ± 1.2
15.0 ± 1.2
12.9 ± 1.2
10.4 ± 1.2
13.9 ± 1.2
16.6 ± 1.2
10.1 ± 1.1
11.0 ± 1.1
12.6 ± 1.1
12.3 ± 1.1
16.5 ± 1.1
10.1 ± 1.1
14.1 ± 1.1
14.2 ± 1.1
15.0 ± 1.1
10.6 ± 1.1
10.9 ± 1.1
12.1 ± 1.1
10.2 ± 1.1
13.3 ± 1.1
12.2 ± 1.1
13.6 ± 1.1
13.1 ± 1.1
18.8 ± 1.1
16.6 ± 1.1
11.1 ± 1.1
15.1 ± 1.1
10.2 ± 1.1
64.0 ± 1.2
63.8 ± 1.2
62.4 ± 1.2
63.5 ± 1.2
64.4 ± 1.2
64.4 ± 1.2
65.1 ± 1.2
62.4 ± 1.2
66.8 ± 1.2
65.8 ± 1.2
62.3 ± 1.2
63.0 ± 1.2
63.8 ± 1.2
64.7 ± 1.2
61.4 ± 1.2
62.3 ± 1.2
65.0 ± 1.2
65.3 ± 1.2
65.6 ± 1.1
63.6 ± 1.1
64.3 ± 1.1
63.2 ± 1.1
64.9 ± 1.1
64.2 ± 1.1
64.1 ± 1.1
62.1 ± 1.1
64.1 ± 1.1
60.6 ± 1.1
61.0 ± 1.1
62.8 ± 1.1
61.8 ± 1.1
63.6 ± 1.1
61.5 ± 1.1
62.7 ± 1.1
63.3 ± 1.1
64.6 ± 1.1
64.8 ± 1.1
65.3 ± 1.1
62.8 ± 1.1
64.4 ± 1.1
168.42
28.81
37.48
75.24
28.96
37.43
76.57
47.83
60.75
60.61
25.41
28.97
37.48
75.52
48.14
75.78
77.00
168.67
145.94
25.89
25.62
76.87
77.15
48.42
25.89
111.76
60.92
146.17
112.03
49.52
49.26
133.19
133.09
25.84
133.36
112.08
156.64
156.56
271.92
156.83
3.15
0.34
3.24
2.81
2.32
3.07
4.89
3.43
1.74
4.00
0.26
2.24
3.07
4.64
3.80
5.08
4.81
2.50
3.94
3.13
3.92
4.88
4.61
0.55
3.67
5.88
0.50
3.92
6.05
0.55
0.55
4.01
6.29
3.93
6.41
6.03
4.67
6.56
3.03
6.69
Comments
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Partially blended
Notes.
a T ∗ and η pertain to frequencies <172 GHz (12 m data), and T ∗ and η apply to frequencies >210 GHz (SMT observations).
R
c
A
b
b Transition frequency measured in laboratory (e.g., Ilyushin & Lovas 2007); lines not marked are predicted using the determined spectroscopic constants.
contamination by other species from known spectral-line
databases (Lovas 2004; Pickett et al. 1998; Müller et al. 2005).
There are no missing transitions, i.e., emission is present at all
favorable transitions with no internal inconsistencies among the
data set. The energy range covered in the identified lines is Eu =
6–818 K (4–568 cm−1 ), with J = 0–27 and Ka = 0–4 from all
symmetry states (A1 , A2 , B1 , B2 , E1 , and E2 ). All of the lines in
the range 0–10 K appear in emission, in contrast to CH2 NH.
An energy level diagram for CH3 NH2 is displayed in Figure 4,
showing levels up to 190 K in energy for J = 0–12 and Ka =
0–3. The observed transitions are marked with arrows. Thirteen
of these lines were also seen by Nummelin et al. (1998). All
of the symmetry components are indicated on the diagram, and
collapse into a single level. The energies of the eight symmetry
components usually only differ by less than 1 K, except for
transitions with J 7 and Ka = 1. Here the states begin to
noticeably split into two levels (A2 , B2 , E1−1 , and E2−1 and A1 ,
B1 , E1+1 , and E2+1 for even J values, and A1 , B1 , E1−1 , and
E2−1 and A2 , B2 , E1+1 , and E2+1 for odd J values) with energy
differences near 3 K; see Figure 4.
Representative spectra of CH3 NH2 are presented in Figure 5.
Spectral resolution is 1 MHz, and the quantum numbers and
rest frequencies are displayed for each transition. The data are
ordered in increasing frequency starting with the top panel of
Figure 5(a), where the JKa Γ = 61 E1−1 → 60 E1−1 transition is
displayed. The CH3 NH2 features are indicated by arrows on
the spectra near VLSR = 62 km s−1 . Additional spectra of both
CH2 NH and CH3 NH2 will be presented elsewhere with the
entire survey (D. T. Halfen et al., in preparation).
The individual, distinguishable emission lines for CH2 NH
and CH3 NH2 were fit with Gaussian profiles and their line parameters (the intensity in TR ∗ or TA ∗ , the linewidth ΔV1/2 , and
the source velocity VLSR ) were determined, as listed in Tables 1
and 2, respectively, along with their uncertainties. Line
6
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Figure 2. Energy level diagram of methanimine, with arrows showing the
transitions observed in this work, as well as those from Sutton et al. (1991)
and Remijan et al. (2008). The levels are separated into Ka ladders to illustrate
the a- and b-type rotational transitions present in this molecule. Each level is
labeled by the quantum numbers JK a ,K c . Several lines are observed in absorption,
as indicated by the arrow direction.
was analyzed by this method for CH2 NH. The following equation was employed for the analysis (Turner 1991):
log
Figure 1. Diagram of the Sgr B2 complex centered near Sgr B2(M) at α =
17h 44m 11s , δ = −28◦ 22 00 (B1950.0), showing the positions of Sgr B2(N),
(M), (OH), (S), (NW), and (2N). The locations, as indicated by the beam sizes,
of the previous detections of methanimine and methyl amine are shown as solid
and dashed circles, with N, S, K, T, and F for Nummelin et al. (1998), Sutton
et al. (1991), Kaifu et al. (1974, 1975), Turner (1989), and Fourikis et al. (1974,
1977), respectively. The current study is shown with bolded solid and dashed
circles, and is labeled with H. The data indicate that methanimine appears to be
present in a ∼3 × 2 region across the Sgr B2 region, and the distribution of
methyl amine covers an area of ∼4 × 2.5 in this complex.
3kTR ΔV1/2
Ntot
Eu log e
= log
−
.
ζrot
k Trot
8π 3 νμ20 Sij
(2)
In the expression, ν is the frequency of the transition, μ0 is
the permanent dipole moment, ζ rot is the rotational partition
function, Sij is the line strength, Eu is the upper state energy,
and TR and ΔV1/2 are the radiation temperature and line widths
(in km s−1 ), respectively. A uniform filling factor was assumed.
As is evident from the past data and illustrated in Figure 1, the
distributions of both CH2 NH and CH3 NH2 are not confined to
Sgr B2(N), but are extended across a large fraction of the Sgr B2
cloud complex. Hence, it is logical to assume that the source
fills the telescope beam in both cases.
The resulting plots are given in Figures 6 and 7. For CH2 NH,
the analysis yields a rotational temperature of Trot = 44 ± 13 K,
with a column density of Ntot = (9.1 ± 4.4) × 1014 cm−2 (see
Figure 6). For CH3 NH2 , a rotational temperature of Trot = 159 ±
30 K and a column density of Ntot = (5.0 ± 0.9) × 1015 cm−2
were derived. As shown in the figures, the CH3 NH2 data
produced much more point-to-point scatter at lower energies
than the CH2 NH data, perhaps due to the lower signal-tonoise ratio for some of the weaker transitions and possible
low-level contamination. The data for the CH2 NH rotational
diagram are quite consistent with low residuals about the fit.
Given a molecular hydrogen column density of 3 × 1024 cm−2
(Nummelin et al. 2000), the fractional abundances of CH2 NH
and CH3 NH2 are ∼3.0 × 10−10 and ∼1.7 × 10−9 , respectively.
parameters for CH2 NH are VLSR = 64.2 ± 1.4 km s−1 and
ΔV1/2 = 13.8 ± 2.8 km s−1 ; for methyl amine, VLSR = 63.7 ±
1.6 km s−1 and ΔV1/2 = 15.1 ± 3.0 km s−1 . These values are typical of organic molecules in Sgr B2(N). For example, acetaldehyde (CH3 CHO), ketene (H2 CCO), and ethanol (C2 H5 OH) have
velocities of VLSR = 64, 63, and 62 km s−1 with linewidths of
ΔV1/2 = 13, 11, and 13 km s−1 (Nummelin et al. 1998; D. T.
Halfen et al., in preparation).
5. DISCUSSION
5.1. Column Densities and Abundances for
Methanimine and Methyl Amine
The column densities Ntot of both CH2 NH and CH3 NH2 were
established by using the rotational temperature diagram method,
which assumes local thermodynamic equilibrium (LTE) and optically thin emission. Only the warm, emission line component
7
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Figure 4. Energy level diagram of methyl amine, displaying the transitions
observed in this work. The levels are separated into Ka ladders to display the
a- and c-type rotational transitions in this molecule. All symmetry components
appear as a single energy level on the diagram because the typical separation is
only 1 K or less. The Ka = 1 components at higher J, however, separate into
the A1 , B1 , E1+1 , and E2+1 states (higher-lying levels) and the A2 , B2 , E1−1 , and
E2–1 levels (lower-lying levels), with a typical energy difference of 3.3 K. Each
level is labeled by the quantum numbers JK a .
Figure 3. Representative spectra of methanimine observed toward Sgr B2(N)
with the ARO 12 m telescope at 2 and 3 mm and the ARO SMT at 1 mm.
Temperature scales are TR ∗ and TA ∗ , respectively. Quantum numbers and rest
frequencies are shown for each spectrum. The transitions are indicated by arrows
and appear near an LSR velocity of 62 km s−1 . The spectral resolution is 1 MHz
or 2.2–1.1 km s−1 over the range 133.7–266.3 GHz. The JK a ,K c = 111 ← 000
transition near 225.5 GHz is observed in absorption, while the other features
appear in emission.
Note that both molecules have similar dipole moments. This
dissimilar distribution and the large difference in the rotational
temperatures between CH2 NH and CH3 NH2 (44 versus 159 K)
suggest that these molecules do not exist in the same gas in
Sgr B2(N). Therefore, it would seem unlikely that CH2 NH is
the synthetic precursor of CH3 NH2 in Sgr B2, as described in
Equation (1).
A grain-surface route to CH3 NH2 was suggested by Garrod
et al. (2008):
Nummelin et al. (2000) published abundances for CH2 NH
and CH3 NH2 of ∼1 × 10−8 and ∼3 × 10−7 for Sgr B2(N),
about 2 orders of magnitude higher than our values. This
discrepancy arises from the small source sizes assumed for these
two molecules by these authors, who used beam-filling factors
of 0.014 for CH2 NH and 0.0022 for CH3 NH2 at the N position.
In contrast, these authors assumed a filling factor of 1 at the M
position (Nummelin et al. 2000); they also did a calculation for
CH3 NH2 in Sgr B2(N) with a uniform filling factor. In these
two cases, they derived abundances of ∼1.4 × 10−10 and ∼2.6
× 10−9 for CH2 NH in Sgr B2(M) and CH3 NH2 in Sgr B2(N),
with rotational temperatures of 44 and 148 K, respectively, in
very good agreement with the values determined here.
CH3 + NH2 → CH3 NH2 .
(3)
However, their gas-grain model for molecular clouds predicts
a gas-phase abundance of CH3 NH2 , with respect to H2 , of
(2–8) × 10−7 , about 2 orders of magnitude higher than that
found here. Hence, these grain reactions leading to CH3 NH2
cannot be significant.
In the HCN hydrogenation route postulated to form CH3 NH2
by Theulé et al. (2011), CH2 NH could not be identified as an
intermediate. These authors concluded that the hydrogenation
steps from CH2 NH to CH3 NH2 had high cross-sections and
fast rate constants. This result suggests that CH2 NH is a trace
intermediate in this process. Hence, if CH3 NH2 is produced on
grains from the hydrogenation of HCN, then the CH2 NH created
in this scheme would be highly underabundant and would not
likely have a discernible gas-phase component. Turner et al.
5.2. Implications for Interstellar Chemistry
The absorption and emission features observed for CH2 NH
suggest that this species exists in both cold, foreground gas and
a warmer, background cloud. The lack of absorption features
in the lowest energy transitions of the CH3 NH2 data and its
higher rotational temperature indicate that this compound is
not significantly present in such cold, foreground material.
8
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
(a)
(b)
Figure 5. Representative spectra of methyl amine observed towards Sgr B2(N) with the ARO 12 m telescope at 2 and 3 mm and the ARO SMT at 1 mm. Temperature
scales are TR ∗ and TA ∗ , respectively. The transitions are indicated with arrows near an LSR velocity of 62 km s−1 . The quantum numbers, symmetry components,
and rest frequencies are displayed on the spectra. The spectral resolution is 1 MHz or 4.1–1.2 km s−1 over the range 72.6–250.7 GHz. (a) Lower frequency transitions
from 72.6 to 134.6 GHz and (b) higher-lying features from 137.6 to 250.7 GHz.
(1999) also concluded that hydrogenation reactions would only
produce the saturated CH3 NH2 and not CH2 NH.
Given the observational data, formation of CH2 NH likely
occurs in the gas phase. Turner et al. (1999) suggested that
CH2 NH was produced through a sequence beginning with the
ion–molecule reaction:
CH+3 + NH2 → CH4 N+ + H.
Given its lower rotational temperature and detection in the cold
core Sgr B2(NW) (see Figure 1), CH2 NH must be present
in cooler gas than methyl amine. It is interesting to note that
CH2 NH has not been detected in the cold, dark cloud TMC-1
(Dickens et al. 1997; Turner et al. 1999). However, it has been
observed in several warmer, molecular clouds, as mentioned. In
cold, dark clouds such as TMC-1, ion–molecule reactions, for
example Equation (4), would be the only viable mechanism
leading to CH2 NH. In the warmer sources, neutral–neutral
processes would also be possible. Synthesis by neutral–neutral
reactions would explain the presence of CH2 NH in only warmer
regions, including Sgr B2(N).
From the past observations, it is obvious that CH3 NH2 is
not confined to the Sgr B2(N) hot core (see Figure 1), but is
widespread throughout the Sgr B2 cloud complex. Given its
high rotational temperature, it must be present near the hot core
gas in Sgr B2(N). A possible synthetic route to CH3 NH2 is the
neutral–neutral reaction:
(4)
The proposed rate is 1 × 10−9 cm3 s−1 . This process is then
followed by dissociative electron recombination, leading to
CH2 NH. Another possible route proposed by Turner et al. (1999)
is a neutral–neutral reaction:
CH3 + NH2 → CH2 NH + H2 .
(5)
These authors suggested this process would have a rate of 1 ×
10−10 cm3 s−1 . Bocherel et al. (1996) experimentally measured
the rate for a similar reaction synthesizing CH2 NH:
CH + NH3 → CH2 NH + H.
CH3 + NH3 → CH3 NH2 + H.
(6)
They determined that the rate for this process is in the range
∼(2–3) × 10−10 cm3 s−1 over the temperature range 23–170 K.
(7)
Because CH3 is a radical, this process could have a rate as
high as ∼10−10 cm3 s−1 (Woodall et al. 2007). The enhanced
9
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
14
Halfen, Ilyushin, & Ziurys
Rotational Temperature Diagram for CH2NH
13
log (3kW/8
3
S 2)
Trot = 44 ± 13 K
Ntot = 9.1 ± 4.4 x 1014 cm-2
12
11
10
0
20
40
60
80
100
120
140
Eu (K)
Figure 6. Rotational temperature diagram of methanimine in Sgr B2(N) constructed from the uncontaminated transitions, assuming the source fills the telescope
beams. The analysis indicates Ntot = (9.1 ± 4.4) × 1014 cm−2 and Trot = 44 ± 13 K. The error bars on the data reflect the uncertainties in the measured integrated
intensities of the spectral lines.
15
Rotational Temperature Diagram for CH3NH2
14
Trot = 159 ± 30 K
Ntot = 5.0 ± 0.9 x 1015 cm-2
WstS 2)
13
log (3kW/8
3
12
11
10
9
8
0
100
200
300
400
500
600
700
800
900
Eu (K)
Figure 7. Rotational temperature diagram of methyl amine in Sgr B2(N) constructed from the uncontaminated transitions, assuming the source fills the telescope
beams. The data suggest Ntot = (5.0 ± 0.9) × 1015 cm−2 and Trot = 159 ± 30 K. The scatter at lower energies likely arises from poorer signal-to-noise ratio data of
weaker transitions and possible low-level contamination. The error bars on the data reflect the uncertainties in the measured integrated intensities of the spectral lines.
(A color version of this figure is available in the online journal.)
temperature found in the Sgr B2(N) core could also help
overcome any small barrier to this process.
Both CH3 NH2 and glycine (NH2 CH2 COOH) have been detected in meteorites, suggesting a possible synthetic connection.
CH3 NH2 has been found to be relatively abundant in Murchison
(Pizzarello et al. 1994), while NH2 CH2 COOH has been identified in multiple meteorites (e.g., Ehrenfreund et al. 2001). Isotopic studies of meteoritic NH2 CH2 COOH (Pizzarello & Huang
10
The Astrophysical Journal, 767:66 (11pp), 2013 April 10
Halfen, Ilyushin, & Ziurys
Fourikis, N., Takagi, K., & Saito, S. 1977, ApJL, 212, L33
Fuchs, G. W., Cuppen, H. M., Ioppolo, S., et al. 2009, A&A, 505, 629
Garrod, R. T., Wakelam, V., & Herbst, E. 2007, A&A, 467, 1103
Garrod, R. T., Widicus Weaver, S. L., & Herbst, E. 2008, ApJ, 682, 283
Godfrey, P. D., Brown, R. D., Robinson, B. J., & Sinclair, M. W. 1973, ApL,
13, 119
Herbst, E., & Klemperer, W. 1973, ApJ, 185, 505
Hershberger, W. D., & Turkevich, J. 1947, PhRv, 71, 554
Ilyushin, V. V., Alekseev, E. A., Dyubko, S. F., Motiyneko, R. A., & Hougen, J.
T. 2005, JMoSp, 229, 170
Ilyushin, V. V., & Lovas, F. J. 2007, JPCRD, 36, 1141
Johnson, D. R., & Lovas, F. J. 1972, CPL, 15, 65
Jones, P. A., Burton, M. G., Cunningham, M. R., et al. 2008, MNRAS, 386, 117
Jones, P. A., Burton, M. G., Tothill, N. F. H., & Cunningham, M. R.
2011, MNRAS, 411, 2293
Kaifu, N., Morimoto, M., Nagane, K., et al. 1974, ApJL, 191, L135
Kaifu, N., Takagi, K., & Kojima, T. 1975, ApJL, 198, L85
Kivelson, D., & Lide, D. R., Jr. 1957, JChPh, 27, 353
Lee, C.-W., Kim, J.-K., Moon, E.-S., Minh, Y. C., & Kang, H. 2009, ApJ,
697, 428
Lide, D. R., Jr. 1957, JChPh, 27, 343
Lovas, F. J. 2004, JPCRD, 33, 177
Millar, T. J., Farquhar, P. R. A., & Willacy, K. 1997, A&AS, 121, 139
Müller, H. S. P., Schloder, S. F., Stutzki, J., & Winneswisser, G. 2005, JMoSt,
742, 215
Nishikawa, T. 1957, JPSJ, 12, 668
Nummelin, A., Bergman, P., Hjalmarson, A., et al. 1998, ApJS, 117, 427
Nummelin, A., Bergman, P., Hjalmarson, Å., et al. 2000, ApJS, 128, 213
Ohashi, N., & Hougen, J. T. 1987, JMoSP, 121, 474
Ohashi, N., Takagi, K., Hougen, J. T., Olson, W. B., & Lafferty, W. J. 1987,
JMoSp, 126, 443
Pickett, H. M., Poynter, R. L., Cohen, E. A., et al. 1998, JQSRT, 60, 883
Pizzarello, S., Feng, X., Epstein, S., & Cronin, J. R. 1994, GeCoA, 58, 5579
Pizzarello, S., & Huang, Y. 2005, GeCoA, 69, 559
Qin, S.-L., Wu, Y., Huang, M., et al. 2010, ApJ, 711, 399
Remijan, A. J., Hollis, J. M., Jewell, P. R., & Lovas, F. J. 2008, BAAS, 40, 188
Salter, C. J., Ghosh, T., Catinella, B., et al. 2008, AJ, 136, 389
Snyder, L. E., Lovas, F. J., Friedel, D. N., et al. 2005, ApJ, 619, 914
Sutton, E. C., Jaminet, P. A., Danchi, W. C., & Blake, G. A. 1991, ApJS,
77, 255
Takagi, T., & Kojima, T. 1971, JPSJ, 30, 1145
Takagi, T., & Kojima, T. 1973, ApJL, 181, L91
Tenenbaum, E. D., Dodd, J. L., Milam, S. N., Woolf, N. J., & Ziurys, L. M.
2010, ApJL, 720, L102
Theulé, P., Borget, F., Mispelaer, F., et al. 2011, A&A, 534, A64
Tielens, A. G. G. M., & Charnley, S. B. 1997, OLEB, 27, 23
Tielens, A. G. G. M., & Hagen, W. 1982, A&A, 114, 245
Turner, B. E. 1989, ApJS, 70, 539
Turner, B. E. 1991, ApJS, 76, 617
Turner, B. E., Terzieva, R., & Herbst, E. 1999, ApJ, 518, 699
Vuitton, V., Yelle, R. V., & McEwan, M. J. 2007, Icar, 191, 722
White, G. J., Araki, M., Greaves, J. S., Ohishi, M., & Higginbottom, N. S.
2003, A&A, 407, 589
Woodall, J., Agúndez, M., Markwick-Kemper, A. J., & Millar, T. J. 2007, A&A,
466, 1197
Yamamoto, S., & Saito, S. 1992, JChPh, 96, 4157
2005) have found deuterium enrichment in this molecule that
suggests an interstellar origin. Isotopic evaluations of CH3 NH2
extracted from meteorites have not yet been carried out, so it is
unclear if this compound represents pristine interstellar material. Additional studies of meteorites and molecular clouds must
be conducted to establish a link between CH2 NH, CH3 NH2 , and
NH2 CH2 COOH.
6. CONCLUSION
Methanimine and methyl amine have been investigated toward the giant molecular cloud Sgr B2(N). The distribution of
both species appears to be extended across the Sgr B2 complex
from the OH to N positions and not exclusively confined to
the hot cores. CH2 NH is present in cold, foreground gas near
Sgr B2(N), as well, where CH3 NH2 is not found. An analysis of
the data demonstrates that these two molecules are quite prevalent in this source, but not as abundant as previously reported.
Furthermore, CH3 NH2 was found to have a much higher rotational temperature than CH2 NH and clearly exists in warmer
gas. These results suggest that these molecules are not directly
connected synthetically, in contrast to the predictions of grain
models. Surface chemistry calculations also fail to predict the
abundances of CH2 NH and CH3 NH2 within several orders of
magnitude. Given the results of this study, there is sparse evidence that these two species are produced from HCN via surface
hydrogenation reactions. Both CH2 NH and CH3 NH2 are more
likely a result of gas-phase neutral–neutral chemistry. Observations of these species in other molecular clouds would be helpful
in providing additional insight into their formation mechanisms.
We thank the staff of ARO for making these observations
possible. This work was supported by NASA Exobiology Grant
NNX10AR83G and NSF URO grant AST-1140030.
REFERENCES
Allegrini, M., Johns, J. W. C., & McKellar, A. R. W. 1979, JChPh, 70, 2829
Aylward, N., & Bofinger, N. 2001, OLEB, 31, 481
Bocherel, P., Herbert, L. B., Rowe, B. R., et al. 1996, JPhCh, 100, 3063
Bossa, J. B., Duvernay, F., Theulé, P, et al. 2009, A&A, 506, 601
Danger, G., Borget, F., Chomat, M., et al. 2011, A&A, 535, A47
Dickens, J. E., Irvine, W. M., DeVries, C. H., & Ohishi, M. 1997, ApJ, 479, 307
Dore, L., Bizzocchi, L., & Degli Esposti, C. 2012, A&A, 544, A19
Dore, L., Bizzocchi, L., Degli Esposti, C., & Gauss, J. 2010, JMoSp, 263, 44
Ehrenfreund, P., Glavin, D. P., Botta, O., Cooper, G., & Bada, J. L. 2001, PNAS,
98, 2138
Fourikis, N., Takagi, K., & Morimoto, M. 1974, ApJL, 191, L139
11