Journal of Molecular Spectroscopy 236 (2006) 11–15
www.elsevier.com/locate/jms
Sub-millimeter spectroscopy of BaS (X1R+)
A. Janczyk, L.M. Ziurys
*
Departments of Chemistry and Astronomy, Steward Observatory, 933 N. Cherry Avenue, University of Arizona, Tucson, AZ 85721, USA
Received 3 October 2005; in revised form 22 November 2005
Available online 7 February 2006
Abstract
The pure rotational spectrum of BaS (X1R+) has been recorded in the frequency range 355–396 GHz using direct absorption methods.
Data were recorded for six isotopomers: 138Ba32S, 137Ba32S, 136B32S, 135Ba32S, 134Ba32S, and 138Ba34S, in vibrational states ranging from
v = 0 to v = 6. This work is an extension of past microwave and millimeter studies. Revised spectroscopic constants have been established
for the six species. The dissociation energy for 138Ba32S is estimated to be DhcE 42 392 cm1.
2005 Elsevier Inc. All rights reserved.
Keywords: Rotational spectra; Diatomics; Sub-mm/THz; Rotational parameters; Bond lengths; Dissociation energy
1. Introduction
Metal sulfides play an important role in a variety of
scientific areas including catalysis, biochemistry, and
materials science [1,2]. Therefore, examining the bonding in such molecules has been of both experimental
and theoretical interest [2,3]. Because of their possible
astrophysical applications, the alkaline earth sulfides
have received some particular attention by spectroscopists [4,5]. BaS is one of such species that has been
studied.
Clements and Barrow [6] obtained the first spectroscopic
data on barium sulfide, studying absorption band systems.
Shortly thereafter, Melendres et al. [7] conducted radio frequency Stark measurements of the J = 1 rotational level of
BaS, and were able to obtain the dipole moment for this
molecule in the v = 0–2 vibrational states. Microwave data
below 70 GHz were published in 1976 by Tiemann et al. [8].
These authors recorded rotational transitions of the main
barium sulfide isotope. The most extensive work done on
this molecule was by Helms et al. [9], who measured millimeter-wave spectra of six isotopic species of BaS in the frequency range 55–339 GHz; for several of the isotopomers,
*
Corresponding author. Fax: +1 520 621 5554.
E-mail address: [email protected] (L.M. Ziurys).
0022-2852/$ - see front matter 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.jms.2005.11.011
transitions were recorded in the v = 1 and 2 vibrational
states as well as the ground states, enabling very accurate
Durham coefficients to be obtained.
In this paper, we report additional measurements of the
pure rotational spectrum of BaS in the range 358–
394 GHz. This study is an extension of the past work by
Helms et al., and includes the same six isotopic species,
with vibrational satellite features up to v = 6. Here, we
present these new data and revised spectroscopic constants
for barium sulfide.
2. Experimental
The pure rotational spectra of the BaS isotopomers were
measured using one of the millimeter wave spectrometers
of the Ziurys group, which is described elsewhere [10].
Briefly, the radiation sources used are phase-locked Gunn
oscillators combined with Schottky diode multipliers,
which cover the frequency range 65–640 GHz. The reaction
cell is a double pass system with a Broida-type oven. The
radiation is focused through the reaction chamber by a series of Teflon lenses and a polarizing grid, is reflected back
through the cell via a rooftop mirror, and then into the
helium-cooled, InSb hot electron bolometer detector.
BaS was synthesized by the reaction of barium
vapor and H2S, in the course of searching for another
12
A. Janczyk, L.M. Ziurys / Journal of Molecular Spectroscopy 236 (2006) 11–15
molecule BaSH [11]. The metal vapor was created in a
Broida-type oven. A mixture of approximately 1 mTorr
H2S and 5 mTorr argon was introduced into the reaction chamber over the top of the oven. About 10 mTorr
argon was flowed from beneath the oven as a carrier
gas for the metal vapor. A d.c. discharge was not found
essential for the production of BaS, as heat generated
by the Broida-type oven appeared to be sufficient to
promote the reaction.
The BaS lines were identified based on the constants
established by Helms et al. Actual transition frequencies
were measured using pairs of 5 MHz scans, one taken in
increasing frequency and one in decreasing frequency.
These data were fit with Gaussian curves to determine center frequencies.
3. Analysis and discussion
Six isotopic species of BaS were measured in natural
abundance: five containing the different isotopes of barium and one with the 34S isotope. The natural
abundances of these elements are 138Ba:137Ba:136Ba:135Ba:134Ba = 71.7:11.2:7.9:6.6:2.4 and 32S:34S = 95.0:4.2.
For the main isotopic species, transitions arising from
the v = 0 through v = 6 levels were recorded. Because
of the decreasing signal-to-noise, lines from the higher
vibrational states could not be measured for the other
isotopomers. For the least abundant species (134Ba32S
and 138Ba34S), only lines from the v = 0 state were
measured.
In Fig. 1, a composite spectrum covering 1.3 GHz in
range, centered at 360 GHz, is shown. The J = 58 fi 59
transitions of 138Ba32S (v = 3 and 4) and 137Ba32S (v = 4)
are visible, along with the J = 57 fi 58 line of 134Ba32S
BaS Isotopomers
138
Ba32S:v = 3
J=58 → 59
138
Ba32S:v = 4
J=58 → 59
134
Ba32S:v = 0
J=57 → 58
137
*
359.8
*
360.1
Ba32S:v = 4
J=58 → 59
360.4
*
360.7
Frequency (GHz)
Fig. 1. Spectra near 360 GHz showing the J = 58 fi 59 transitions of
138
Ba32S (v = 4 and v = 3) and 137Ba32S (v = 4), as well as the J = 57 fi 58
line of 134Ba32S (v = 0). The lines marked by asterisks are unidentified. The
spectrum covers 1.3 GHz and is a composite of 13,100 MHz scans, each
with a duration of about 1 min.
(v = 0). The intense lines are a result of the high dipole
moment of BaS (l = 10.852 D) and the fact that the molecule is stable under the high temperature conditions present
in the spectrometer.
The transition frequencies measured typically deviated from those predicted by Helms et al. [9] by 1–
10 MHz, with increasing deviation with vibrational
quantum number. Hence, identifying all the spectral
features was an iterative process of fitting detected lines
with the previous data and then predicting higher frequency transitions. The data set thus obtained is listed
in Table 1.
The data were initially fit using the non-linear leastsquares code, SPFIT [12]. Each isotopomer and vibrational state was fit individually and the Bv and Dv
parameters established. (The higher order term Hv was
not found necessary in these fits.) Two different analyses
were carried out: a local fit of the transitions only measured in this work (355–396 GHz), and a global fit that
included the Helms et al. data were well. These values
were then used to establish the equilibrium parameters
for four of the six isotopomers, as defined by the
equations:
2
4
1
1
1
Bv ¼ Be a e m þ
þ þ ge m þ
;
þ ce m þ
2
2
2
1
Dm ¼ De þ be m þ .
2
ð1Þ
ð2Þ
A correction term ge could be determined only for
the main species, 138Ba32S, where six vibrational states
were measured. Equilibrium constants could not be
established for 134Ba32S and 138Ba34S because in these
cases only transitions from the v = 0 state were
recorded.
The spectroscopic parameters established from the
analysis are given in Table 2. There is very little difference between the local and global fits, as the table
shows. Also listed in Table 2 are estimates of the
vibrational constants xe and xeve, as defined by the
expressions [13]:
sffiffiffiffiffiffiffiffi
4B3e
;
ð3Þ
xe ¼
De
2
ae x e
xe ve ¼ Be
þ
1
.
ð4Þ
6B2e
The values obtained for the main isotopomer are in
good agreement with those derived from optical data,
which are xe = 379.42 cm1 and xeve = 0.8842 cm1
[14]. Using the vibrational parameters, the dissociation
energy of BaS was estimated to be DhcE 42 392
(332) cm1.
Using the constants obtained, and the equilibrium
internuclear distance of re = 2.50732 Å, a Morse-type
A. Janczyk, L.M. Ziurys / Journal of Molecular Spectroscopy 236 (2006) 11–15
13
Table 1
Observed rotational transitions of BaS (X1R+)a
J0
v0
J00
v00
58
59
60
61
62
63
64
58
59
60
61
62
63
64
58
59
60
61
62
63
64
58
59
60
61
62
63
64
59
60
61
62
63
64
65
59
60
61
62
63
64
65
59
60
61
62
63
64
65
0
0
0
0
0
0
0
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
6
6
6
6
6
6
6
57
58
59
60
61
62
63
57
58
59
60
61
62
63
57
58
59
60
61
62
63
57
58
59
60
61
62
63
58
59
60
61
62
63
64
58
59
60
61
62
63
64
58
59
60
61
62
63
64
0
0
0
0
0
0
0
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
6
6
6
6
6
6
6
67.5%
0
0
0
0
0
0
0
0
0
0
1
57
58
59
60
61
62
63
64
65
66
57
0
0
0
0
0
0
0
0
0
0
1
Ba32S
10.8%
137
Ba32S
7.4%
136
Ba32S
mobs
mcal mobs
mobs
mcal mobs
mobs
mcal mobs
358018.997
364166.379
370312.413
376457.158
382600.560
388742.589
394883.274
356918.831
363047.169
369174.208
375299.936
381424.301
387547.319
393668.918
355815.591
361924.863
368032.838
374139.488
380244.789
386348.711
392451.236
0.007
0.020
0.014
0.014
0.012
0.015
0.027
0.009
0.002
0.009
0.000
0.007
0.010
0.001
0.005
0.004
0.004
0.001
0.004
0.002
0.002
360799.393
366888.243
372975.749
379061.949
385146.717
391230.107
359670.682
365740.323
371808.644
377875.626
383941.234
390005.416
396068.209
358538.575
364588.963
370638.060
376685.798
382732.137
388777.079
394820.591
357403.031
363434.120
369463.902
375492.331
381519.371
387544.803b
393569.201
0.000
0.000
0.013
0.021
0.002
0.006
0.017
0.005
0.014
0.006
0.006
0.008
0.011
0.014
0.018
0.005
0.007
0.002
0.002
0.002
0.018
0.013
0.011
0.001
0.004
358509.507
364665.213
370819.690
376972.817
383124.570
389274.981
395423.988
357407.052
363543.736
369679.111
375813.189
381945.877
388077.227
394207.167
356301.534
362419.114
368535.390
374650.343
380763.947
386876.153
392986.969
355192.915
361291.318
367388.445
373484.205
379578.613
385671.655
391763.308
360160.248
366238.123
372314.674
378389.860
384463.677
390536.106
0.019
0.027
0.003
0.009
0.009
0.002
0.003
0.011
0.001
0.014
0.006
0.013
0.004
0.007
0.005
0.004
0.007
0.001
0.010
0.001
0.003
0.008
0.009
0.010
0.003
0.011
0.006
0.012
0.012
0.003
0.005
0.012
0.007
0.015
359008.142
365172.402
371335.379
377497.007
383657.296
389816.188
395973.720
357903.365
364048.548
370192.417
376334.966
382476.131
388615.944
394754.348
356795.526
362921.570
369046.310
375169.674
381291.696
387412.341
393531.607
355684.568
361791.398
367896.914
374001.089
380103.901
386205.310
392305.360
0.008
0.007
0.003
0.004
0.003
0.012
0.010
0.001
0.000
0.002
0.009
0.008
0.001
0.000
0.008
0.001
0.019
0.003
0.008
0.011
0.010
0.003
0.001
0.003
0.005
0.004
0.017
0.008
6.3%
58
59
60
61
62
63
64
65
66
67
58
138
135
0.003
32
Ba S
2.3%
134
Ba32S
3.02%
mobs
mcal mobs
mobs
mcal mobs
359512.965
365685.860
371857.429
378027.707
384196.623
390364.160
0.017
0.003
0.025
0.009
0.002
0.013
360026.437
366208.172
372388.559
378567.575
384745.259
390921.540
0.009
0.001
0.014
0.005
0.005
0.006
358405.838
0.015
138
Ba34S
mobs
mcal mobs
358554.238
364406.762
370258.016
376108.035
381956.752
387804.201
393650.312
0.001
0.011
0.007
0.001
0.014
0.005
0.005
(continued on next page)
14
A. Janczyk, L.M. Ziurys / Journal of Molecular Spectroscopy 236 (2006) 11–15
Table 1 (continued)
J0
59
60
61
62
63
64
58
59
60
61
62
63
64
a
b
v0
1
1
1
1
1
1
2
2
2
2
2
2
2
J00
v00
58
59
60
61
62
63
57
58
59
60
61
62
63
1
1
1
1
1
1
2
2
2
2
2
2
2
6.3%
135
Ba32S
2.3%
mobs
mcal mobs
364559.626
370712.072
376863.196
383012.957
389161.331
395308.264
357295.664
363430.243
369563.513
375695.447
381826.009
387955.187
394082.980
0.005
0.001
0.008
0.013
0.013
0.023
0.004
0.003
0.002
0.003
0.003
0.008
0.008
134
Ba32S
mobs
3.02%
mcal mobs
mobs
138
Ba34S
mcal mobs
In MHz.
Contaminated; not included in the fit.
Table 2
Rotational constants for BaS (X1R+)
138
Ba32S
Be (MHz)
ae (MHz)
ce (MHz)
ge (MHz)
De (kHz)
be (Hz)
xe (cm1)
xeve (cm1)
137
Ba32S
Global fit
Local fit
Global fit
Local fit
Global fit
3097.2794(23)
9.4462(25)
0.01305(62)
7.9(7.1) · 106
0.91787(31)
1.838(78)
379.57(19)
0.8495(19)
3097.2822(23)
9.4469(25)
0.01300(60)
8.5(7.0) · 106
0.91826(26)
1.780(63)
379.49(16)
0.8493(21)
3101.5346(42)
9.4645(40)
0.01351(78)
3101.5357(42)
9.4642(39)
0.01363(77)
3105.86290(35)
9.48711(41)
0.01293(10)
3105.8614(38)
9.4842(45)
0.0136(11)
0.92065(23)
1.774(79)
379.78(14)
0.8504(19)
0.92085(20)
1.733(71)
379.73(12)
0.8502(17)
0.92333(30)
1.73(13)
380.02(19)
0.8518(17)
0.92339(20)
1.748(87)
380.01(12)
0.8515(19)
Ba32S
a
b
Ba32S
Local fit
135
Be (MHz)
ae (MHz)
ce (MHz)
De (kHz)
be (Hz)
xe (cm1)
xeve (cm1)
136
134
Ba32S
3110.239(58)
9.501(86)
0.015(27)
0.92603(66)
1.69(39)
380.27(41)
0.852(30)
3110.244(14)
9.508(26)
0.0131(94)
0.926214(74)
1.575(43)
380.229(46)
0.8529(91)
138
Ba34S
a
a
3109.9298(90)
3109.9302(23)
2945.1724(71)a
2945.1741(21)a
0.9294(12)b
0.92949(33)b
0.83354(87)b
0.83375(26)b
B0 in this case.
D0 in this case.
potential was constructed using the following equation
[13]:
2
U ðrÞ ¼ DE ½1 ebðrreÞ ð5Þ
qffiffiffiffiffi
Here b ¼ pxe D2lE , and equals 1.1435 Å1. This potential is plotted in Fig. 2. It suggests that BaS reaches the dissociation limit near 5 Å—twice its equilibrium internuclear
distance. In comparison, CsCl has a dissociation limit near
15 700 cm1 [15], considerably less than that of BaS. This
difference suggests that the bonding in these molecules varies. As mentioned by Tiemann et al. [8], a r covalent bond
likely exists in BaS, while CsCl is predominantly ionic. The
partial covalent character in barium sulfide perhaps is
responsible for the higher dissociation energy.
4. Conclusion
New spectroscopic data have been obtained for six isotopomers of BaS in the sub-millimeter region—an extension of the past microwave and millimeter studies.
Revised rotational constants has been obtained for these
species. From these parameters, vibrational constants have
been calculated from which a dissociation energy has been
A. Janczyk, L.M. Ziurys / Journal of Molecular Spectroscopy 236 (2006) 11–15
15
Acknowledgment
60000
BaS (X1Σ+)
This research is supported by NSF Grant CHE0411551.
References
Energy / hc (cm -1)
42392
D0
30000
DE
15000
0
1.7
2.3
2.9
3.5
4.1
4.7
5.3
Internuclear Distance (Å)
Fig. 2. Morse potential curve for 138Ba32S based on vibrational constants
and internuclear distance derived from the rotational parameters. Energy
is expressed in vacuum wavenumbers, where h is Planck’s constant and c is
the speed of light.
estimated, which is markedly higher than that of isoelectronic CsCl. Some partial covalent character may exist in
BaS.
[1] I. Kretzschmar, D. Schröder, H. Schwarz, P.B. Armentrout, Int. J.
Mass. Spectrom. 228 (2003) 439–456.
[2] I. Kretzschmar, D. Schröder, H. Schwarz, P.B. Armentrout, Adv.
Metal Semicond. Clusters 5 (2001) 347–360.
[3] A.J. Bridgeman, J. Rothery, J. Chem. Soc., Dalton Trans. (2000)
211–218.
[4] S. Takano, S. Yamamoto, S. Saito, Chem. Phys. Lett. 159 (1989)
563–566.
[5] D.T. Halfen, A.J. Apponi, J.M. Thompsen, L.M. Ziurys, J. Chem.
Phys. 115 (2001) 11131–11138.
[6] R.M. Clements, R.F. Barrow, Chem. Commun. (Lond.) 22 (1968)
1408.
[7] C.A. Melendres, A.J. Hebert, K. Street Jr., J. Chem. Phys. 51 (1969)
855–856.
[8] E. Tiemann, Ch. Ryzlewicz, T. Törring, Z. Naturforsch. A 31 (1976)
128–130.
[9] D.A. Helms, M. Winnewisser, G. Winnewisser, J. Phys. Chem. 84
(1980) 1758–1765.
[10] L.M. Ziurys, W.L. Barclay Jr., M.A. Anderson, D.A. Fletcher, J.W.
Lamb, Rev. Sci. Instrum. 65 (1994) 1517–1522.
[11] A. Janczyk, L.M. Ziurys, J. Chem. Phys 119 (2003) 10702–10712.
[12] H.M. Pickett, J. Mol. Spectrosc. 148 (1991) 371–377.
[13] W. Gordy, R.L. Cook, Microwave Molecular Spectra, Wiley, New
York, 1984.
[14] K. Huber, G. Herzberg, Constants of Diatomic Molecules, Van
Nostrand, New York, 1979.
[15] R. Honerjäger, R. Tischer, Z. Naturforsch. A 29 (1974) 819–821.