Chemical Physics Letters 401 (2005) 211–216
www.elsevier.com/locate/cplett
Examining the transition metal hydrosulfides: the pure
~ 1A0 Þ
rotational spectrum of CuSH ðX
A. Janczyk, S.K. Walter, L.M. Ziurys
*
Department of Chemistry, Department of Astronomy, and Steward Observatory 933 N. Cherry Ave.Tucson, AZ 85721-0065, USA
Received 19 July 2004; in final form 23 October 2004
Available online 8 December 2004
Abstract
The pure rotational spectrum of copper hydrosulfide, CuSH, has been recorded using millimeter/sub-millimeter direct absorption
methods. Both copper isotopomers and their deuterated analogs were observed. The molecules were synthesized by the reaction of
H2S or D2S with copper vapor in a dc discharge. For all four isotopomers, multiple transitions were measured, each exhibiting
extensive Ka ladder structure and signifying that CuSH is a near-prolate asymmetric top. Rotational parameters were determined
for the four species, from which a structure has been derived. The Cu–S–H bond angle was found to be 93, similar to other metal
hydrosulfides and H2S, rather than CuOH.
2004 Elsevier B.V. All rights reserved.
1. Introduction
The formation of metal–OH bonds is important in a
wide range of scientific fields, including electrochemistry, corrosion phenomena and in biological processes
[1,2]. As a consequence, the spectra of many alkali and
alkaline earth monohydroxides, as well as AlOH, have
been measured by a variety of techniques [3–9]. These
molecules have been found to be linear or quasilinear
in their ground electronic states, and some are known
to exhibit large amplitude bending motions [10]. In contrast, transition metal monohydroxides have largely
been neglected. Thus far, the spectra of only CuOH
and AgOH have been studied [11–14]. These species
have been found to be bent with angles near 108–110,
the tetrahedral angle, suggestive of some sort of orbital
hybridization.
*
Corresponding author. Fax: 520 621 1532.
E-mail address: [email protected] (L.M. Ziurys).
0009-2614/$ - see front matter 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2004.10.146
The sulfur analogs of the metal monohydroxides, the
hydrosulfides MSH, have varied chemical applications,
from the creation of metalloenzymes to industrial hydrodesulfurization [15]. To date, only alkali and alkaline
earth-bearing molecules of this type have been investigated spectroscopically [16–20]. These species have all
been discovered to be bent with an angle near 90.
The structural variations between the alkali/alkaline
earth monohydroxides and the monohydrosulfides
probably reflect the differences in electronegativity,
orbital energies and atomic radius of oxygen relative
to sulfur.
In this Letter, we present the first gas-phase spectroscopic study of a transition metal hydrosulfide.
~ 1 A0
The pure rotational spectrum of CuSH in its X
ground electronic state was recorded using millimeter/sub-millimeter direct absorption techniques. Spectra of the deuterium isotopomer, CuSD, and the less
abundant copper species, 65CuSH and 65CuSD, were
also measured. These data clearly indicate that CuSH
is bent. Here, we describe our results and compare the
properties of CuSH with other metal hydrosulfides
and hydroxides.
212
A. Janczyk et al. / Chemical Physics Letters 401 (2005) 211–216
2. Experimental
The rotational spectra of CuSH and its isotopomers
were measured using one of the millimeter-wave spectrometers of the Ziurys group, which is described
elsewhere [21]. Briefly, the instrument consists of a
Gunn oscillator/Schottky diode multiplier frequency
source, a gas cell in which the radiation is propagated
quasi-optically, and an InSb bolometer detector.
Phase-sensitive detection is achieved by modulating the
source and signals are detected at 2f.
CuSH was produced by reacting copper vapor with
H2S in the presence of a dc discharge. The vapor was
created using a Broida-type oven. A reaction mixture
of approximately 2 mtorr of H2S and 10 mtorr of argon
carrier gas were added to the metal vapor through an inlet tube located over the top of the oven. To achieve a
more stable discharge, an additional 10 mtorr of argon
was added through the bottom of the oven, as well.
The discharge required approximately 30 mA at 200
V. The presence of copper vapor was easily verified by
a bright green discharge glow. For the production of
CuSD, D2S (Cambridge Isotopes Laboratories) was
used as the reacting gas in the same procedure. The less
abundant copper isotopomer was observed in its natural
abundance (63Cu:65Cu = 69.1:30.9).
Initially, a range of 366–398 GHz was continuously
searched using 100 MHz scans to locate spectra. Actual
transition frequencies were determined from scans 5
MHz in coverage and the resulting spectra fit with a
Gaussian line profile. These scans were always recorded
as pairs, one in increasing and the other in decreasing
frequency, but for some of the weaker Ka components
as many as 16 scans were averaged. Linewidths ranged
from 629 to 1380 kHz, respectively, over the region
260–535 GHz.
mined, which gave sufficiently accurate predictions
that the Ka = 0, 1 and 2 lines could be easily assigned.
For CuSD, a similar frequency range was scanned.
The Ka = 4 lines were initially identified because of their
unusually broad profiles, arising from unresolved asymmetry doubling. The Ka = 3 doublets in this case were
split by 33–85 MHz, and were located on this premise,
and the Ka = 5, 6, 7 and 8 components were assigned
on the basis of their approximate symmetric top pattern.
The remaining features were identified after obtaining
approximate constants and repredicting the spectra.
Lines originating from 65CuSH and 65CuSD, the less
abundant copper isotopomers, were interspersed among
the main isotopic data. The spectral patterns of these
species were very similar to the 63Cu isotopomers. Consequently, once some harmonic relationships were established, the various Ka components of these molecules
were assigned without difficulty.
In Fig. 1, the spectral patterns of all four isotopomers
of CuSH are illustrated for the J = 37
36 transition,
using stick figures that each cover 7.5 GHz in range.
Approximate intensities are shown. As is clear from
these diagrams, the CuSH species have more symmetric
CuSH(X1A′) : J = 37→36 : Ka Components
63
CuSH 1
8
385.5 65
7
0 3
5 42 2
CuSH
1
7
389.3
393.0
1
6
382.5 63
1
0
54 3
6 2 2
386.3
390.0
CuSD
1
0
3. Results
8
Because CuSH had not been studied previously by
experiment or theory, a bent structure was assumed,
which results in an a-type pattern. An effective B value
of B + C/2 5276 MHz was estimated, which turned
out to be quite close to the actual Beff of 5274 MHz.
Consequently, lines originating from CuSH were found
after a few hundred MHz of scanning. However, in order to identify harmonic relationships among the Ka
asymmetry components, approximately 6 Beff in frequency (or 32 GHz) were continuously searched
(366–398 GHz). The Ka = 3 asymmetry components
were initially identified because of their small splittings
of 2–3 MHz. The Ka = 4–8 components, whose asymmetry splitting is totally collapsed, were then found because
of their symmetric-top like pattern. From these six components, preliminary rotational constants were deter-
CuSD
369.5
1
2
3
377.3
373.5 65
1
7
25
6 4
0
54
6
7 2
8
3
381.0
1
2
373.3
377.0
1
Frequency (GHz)
Fig. 1. A stick figure showing the relative intensities and progressions
of the Ka components of the J = 37 36 transition of 63CuSH,
65
CuSH, 63CuSD and 65CuSD. All data is plotted on the same relative
frequency scale. These asymmetric patterns clearly indicate that copper
hydrosulfide is a bent molecule. For 63CuSH and 65CuSH, the Ka = 0
line is located approximately between Ka = 1 asymmetry doublets. In
contrast, the Ka = 0 feature is shifted considerably to the left of the
Ka = 1 centroid for 63CuSD and 65CuSD, indicating a higher degree of
asymmetry in these species.
A. Janczyk et al. / Chemical Physics Letters 401 (2005) 211–216
patterns, with the Ka = 0 feature lying almost at the centroid of the Ka = 1 asymmetry doublets. For the CuSD
isotopomers, the Ka = 0 line is shifted sufficiently far
to lower frequency of this centroid that all subsequent
Ka components (Ka = 2 through 8) appear to the right
(or at higher frequency) of this feature.
Representative spectra are presented in Figs. 2 and 3.
In Fig. 2a, a section of the J = 37
36 transition of
63
CuSH is shown, (a) as well as lines from the
J = 38
37 transition of 65CuSH (b). Both data sets
have cover about 250 MHz in frequency. In the case
of 63CuSH, the Ka = 0, 3 and 4 components are present,
along with one line from the Ka = 2 asymmetry doublet.
One of the two Ka = 3 pairs is barely visible because it
lies between its partner and the Ka = 2 feature. For the
copper 65 isotopomers, the Ka = 0, 3 and 4 lines are visible, as well as one Ka = 2 feature, which is blended with
the higher frequency transition of the Ka = 3 doublet.
In Fig. 3, a section of the J = 36
35 transition of
63
CuSD (a) and the J = 38
37 transition of 65CuSD
(b) are shown. Both spectrum are on approximately
the same relative frequency scale. In the 63CuSD data,
the Ka = 4, 5 and 3 components are present, as well as
one of the Ka = 2 asymmetry doublets. The Ka = 3 pair
is split by about 50 MHz. A very similar pattern appears
in the less abundant copper isotopomer.
~
CuSH ( X1 A′): (Ka,Kc )
(a)
63
CuSH: J=37 →36
(0,37) − (0,36)
(4,33) − (4,32)
+
(4,34) − (4,33)
389.26
(b)
(3,34) − (3,33)
(3,35) − (3,34)
389.36
389.46
65
CuSH: J=38 →37
(0,38) − (0,37)
395.56
(2,36) − (2,35)
(4,34) − (4,33)
+
(4,35) − (4,34)
(2,37) − (2,36)
+
(3,35) − (3,34)
(3,36) − (3,35) ∗
395.66
395.76
Frequency (GHz)
Fig. 2. Spectrum of a section of the J = 37 36 transition of 63CuSH
near 389 GHz (a) and of the J = 38 37 transition of 65CuSH near
395 GHz (b). Frequency scales are identical. Various asymmetry
doublets are visible, indicated by (Ka, Kc) quantum numbers. Some
doublets are collapsed. An asterisk marks an unidentified line. These
spectra are a composite of three 100 MHz scans, each with an
acquisition time of 60 s.
213
~
CuSD ( X1 A′): (Ka,Kc )
(a)
(2,35) − (2,34)
(5,31) − (5,30)
+
(5,32) − (5,31)
367.15
(b)
(4,32) − (4,31) 63CuSD:
+
(4,33) − (4,32)
(3,34) − (3,33)
367.38
J=36 →35
(3,33) − (3,32)
367.60
65
CuSD: J=38 →37
(5,33) − (5,32)
+
(5,34) − (5,33) (4,34) − (4,33)
(3,35) − (3,34)
(2,37) − (2,36)
+
(4,35) − (4,34) (3,36) − (3,35)
∗
383.38
383.58
Frequency (GHz)
383.78
Fig. 3. Spectrum of a portion of the J = 36 35 transition of 63CuSD
near 367 GHz (a) and the J = 38 37 transition of 65CuSD near 383
GHz (b). Various asymmetry components are present in each
spectrum, some which appear as doublets and several which are
collapsed into single lines. The spectra are both approximately on the
same relative frequency scale, and unidentified features are indicated
by asterisks. These spectra were constructed from five, 100 MHz scans,
each with an acquisition time of 60 s.
A subset of the transition frequencies recorded for the
four isotopomers of CuSH are given in Tables 1 and 2.
(See
www.chem.arizona.edu/faculty/Ziur/Ziur-group.
html for the complete data set.) As the tables show,
asymmetry components in the range Ka = 0 to Ka = 8
were usually measured per transition. For Ka P 4, the
asymmetry doubling was collapsed or nearly collapsed,
so only one frequency appears. The data were measured
over the range J00 = 24–50 for the CuSH species (259–
540 GHz) and J00 = 32 through 39 (330–412 GHz) for
the CuSD isotopomers. In all, ten and six transitions
were recorded for 63CuSH and 65CuSH, respectively,
for a total of 111 and 63 individual measurements.
For the deuterium counterparts, a total of six and five
transitions were measured, corresponding to 72 and 60
separate lines.
4. Analysis
All four data sets of CuSH were analyzed using an Sreduced Hamiltonian, which was incorporated into
SPFIT, a non-linear least-squares code developed by
Pickett [22]. The resulting spectroscopic constants for
the four isotopomers are given in Table 3. The individual rms values of the fits lie in the range 27–38 kHz.
Nine to ten constants were required to fit each molecule
214
A. Janczyk et al. / Chemical Physics Letters 401 (2005) 211–216
Table 1
Selected rotational transitions of
63
CuSH, and
~ 1 A0 Þa
CuSH ðX
65
J0
K 0a
K 0c
J00
K 00a
K 00c
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
36
36
36
36
36
36
36
36
36
36
36
36
36
36
36
36
36
1
8
8
7
7
6
6
5
5
4
4
0
3
3
2
2
1
1
8
8
7
7
6
6
5
5
0
4
4
3
3
2
2
1
25
18
17
19
18
20
19
21
20
22
21
25
23
22
24
23
24
36
29
28
30
29
31
30
32
31
36
33
32
34
33
35
34
35
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
35
1
8
8
7
7
6
6
5
5
4
4
0
3
3
2
2
1
1
8
8
7
7
6
6
5
5
0
4
4
3
3
2
2
1
24
17
16
18
17
19
18
20
19
21
20
24
22
21
23
22
23
35
28
27
29
28
30
29
31
30
35
32
31
33
32
34
33
34
a
b
63
65
CuSH
CuSH
mobs
mobs mcalc
mobs
mobs mcalc
262181.426
262887.207
262887.207
263030.315
263030.315
263154.625
263154.625
263260.334
263260.334
263347.932
263347.932
263422.485
263418.917b
263418.917b
263445.703
263517.889
264754.080
377128.754
378169.939
378169.939
378375.693
378375.693
378554.775
378554.775
378707.796
378707.796
378823.752
378836.140
378836.140
378943.289
378945.572
378950.624
379164.709
380815.844
0.019
0.052
0.052
0.038
0.038
0.001
0.001
0.025
0.025
0.009
0.010
0.008
259451.648
0.001
260282.696
260282.696
260404.453
260404.453
260507.865
260507.865
260593.451
260593.451
260668.045
260662.857b
260662.857b
260689.437
260758.693
261970.775
373206.794
0.046
0.046
0.058
0.058
0.030
0.030
0.048
0.049
0.045
374427.098
374427.098
374602.335
374602.335
374752.008
374752.008
374869.967
374877.518
374877.518
374982.177
374984.357
374990.569
375195.830
376817.531
0.004
0.004
0.011
0.011
0.014
0.014
0.030
0.003
0.006
0.006
0.027
0.026
0.001
0.015
0.017
0.018
0.006
0.012
0.025
0.025
0.030
0.030
0.014
0.014
0.011
0.010
0.007
0.015
0.006
0.005
0.001
0.017
0.015
0.005
0.040
0.023
0.008
0.008
In MHz, for v = 0.
Blended lines; not included in fit.
– a much smaller number of parameters than those used
for LiSH, SrSH, BaSH [18–20]. Only two to three sixthorder terms were needed to obtain an adequate fit for
the CuSH species. In comparison, three eight-order
(LJK, LJJK and LKKJ) and one 10-order (PKJ) terms were
found necessary for an equivalent rms for LiSH. This result suggests that CuSH is a more rigid molecule than
the alkali/alkaline earth hydrosulfides.
Three types of structures could be determined for
ð1Þ
CuSH: r0, rs and rm
[23]. A least-squares fit to all twelve
moments of inertia resulted in rCu–S = 2.091 Å,
rS–H = 1.35 Å and hCu–S–H = 93 for the r0 structure;
the rs calculation yielded rCu–S = 2.0899 Å, rS–H = 1.32
Å, with an angle of 94.2, using an average of three
isotopomer combinations and the moment of inertia
condition to locate the sulfur atom. A least-squares fit
ð1Þ
gave an rm
structure of rCu–S = 2.0908 Å, rS–H = 1.353
Å and hCu–S–H = 93.5. These structures are presented
in Table 4.
5. Discussion
This study has clearly established that CuSH has a
bent geometry with an angle near 93. This angle differs
significantly from that in CuOH, which is near 110.
The tetrahedral angle is 109.5; therefore, it appears that
CuOH bonds via sp3 hybridization of the oxygen orbitals, in analogy to water. CuSH, on the other hand, seems
to bond through simple p-orbitals, similar to H2S, hence
the near 90 angle. Thus, the substitution of the oxygen
atom with sulfur significantly alters the nature of the
bonding in these species. Because oxygen is the more electronegative atom, electrostatic repulsion may be forcing
a tetrahedral geometry in order to achieve maximum distance between lone pairs and bonds. This situation is evidently not as critical for CuSH.
Table 4 also displays r0 structures of other metal
hydrosulfides. As shown in the table, the bond angle of
CuSH (93–94) is identical to those of LiSH and NaSH
A. Janczyk et al. / Chemical Physics Letters 401 (2005) 211–216
Table 2
Selected rotational transitions of
63
CuSD and
1
CuSD ðX~ A0 Þa
65
J0
K 0a
K 0c
J00
K 00a
K 00c
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
39
39
39
39
39
39
39
39
39
39
39
39
39
39
39
39
39
1
0
8
8
7
7
6
6
5
5
2
4
4
3
3
2
1
1
0
8
8
7
7
6
6
2
5
5
4
4
3
3
2
1
33
33
26
25
27
26
28
27
29
28
32
30
29
31
30
31
32
39
39
32
31
33
32
34
33
38
35
34
36
35
37
36
37
38
32
32
32
32
32
32
32
32
32
32
32
32
32
32
32
32
32
38
38
38
38
38
38
38
38
38
38
38
38
38
38
38
38
38
1
0
8
8
7
7
6
6
5
5
2
4
4
3
3
2
1
1
0
8
8
7
7
6
6
2
5
5
4
4
3
3
2
1
32
32
25
24
26
25
27
26
28
27
31
29
28
30
29
30
31
38
38
31
30
32
31
33
32
37
34
33
35
34
36
35
36
37
a
b
215
63
65
CuSD
CuSD
mobs
mobs mcalc
mobs
mobs mcalc
333669.843
335920.225
336255.009
336255.009
336423.340
336423.340
336572.807
336572.807
336705.978
336705.978
336720.747
336829.801
336829.801
336950.429
336983.108
337728.205
339656.368
393988.737
396309.193
397147.751
397147.751
397348.393
397348.393
397528.114
397528.114
397608.961
397691.360
397691.360
397849.395b
397849.395b
398002.085
398077.054
399228.717
401008.150
0.019
0.041
0.006
0.006
0.018
0.018
0.032
0.032
0.004
0.001
0.036
0.196
0.208
0.004
0.046
0.005
0.002
0.013
0.011
0.009
0.009
0.002
0.002
0.001
0.001
0.015
0.020
0.008
330176.962
332395.536
332703.635b
332703.635b
332867.790
332867.790
333013.796
333013.796
333143.825
333143.825
333162.574
333264.469
333264.469
333381.811
333412.558
334128.777
336039.118
389869.728
392165.225
392955.038
392955.038
393151.175
393151.175
393326.710
393326.710
393412.430
393485.964
393485.964
393639.683b
393639.683b
393788.500
393858.868
394967.327
396745.024
0.003
0.027
0.000
0.009
0.018
0.022
0.036
0.036
0.018
0.018
0.006
0.008
0.022
0.215
0.155
0.043
0.015
0.022
0.014
0.002
0.004
0.006
0.006
0.032
0.032
0.023
0.023
0.012
0.044
0.034
0.009
0.059
0.017
0.030
In MHz, for v = 0.
Blended lines; not included in fit.
Table 3
1
Spectroscopic constants for CuSH ðX~ A0 Þ isotopomersa
63
CuSH
65
63
CuSH
CuSD
65
CuSD
A
B
C
DJ
DJK
d1
d2
HJ
HJJK
HJKK
288887(54)
5326.6603(30)
5223.3335(29)
0.00406957(96)
0.191511(44)
0.00008137(46)
5.98(19) · 106
5.7(1.9) · 1010
6.572(78) · 107
3.04(65) · 106
288864(86)
5270.3283(74)
5169.1571(73)
0.00398687(83)
0.18738(12)
0.0000785(13)
5.73(30) · 106
149584.9(9.9)
5205.1176(99)
5021.4735(94)
0.0037858(10)
0.16605(14)
0.0001427(16)
1.791(24) · 105
149582(11)
5148.980(11)
4969.203(10)
0.0037072(11)
0.16238(14)
0.0001384(17)
1.718(26) · 105
6.21(37) · 107
3.3(1.5) · 106
6.81(38) · 107
2.39(77) · 106
6.40(48) · 107
2.05(85) · 106
Rms of fit
0.034
0.033
0.027
0.038
a
In MHz; errors are 3r.
[19,24]. The bond angle of the open-shell hydrosulfides is
somewhat smaller (88–91), probably because of repulsion between the free electron on the metal atom and the
lone pairs on sulfur. These angles are all close to that of
H2S, and there is little evidence of orbital hybridization
in these species. Within the quoted errors, the S–H bond
lengths are virtually identical, falling in the range 1.353–
1.360 Å, while the metal–sulfur bond lengths increase
216
A. Janczyk et al. / Chemical Physics Letters 401 (2005) 211–216
Table 4
Structures for metal hydrosulfide speciesa
M–SH
Ground state
rM–S (Å)
rS–H (Å)
hM–S–H (deg)
References
CuSH
1
LiSH
NaSHc
MgSH
CaSH
SrSH
BaSH
1
2.091(2)
2.0899(4)
2.0908(3)
2.146(1)
2.479(1)
2.316(15)
2.564(6)
2.706(3)
2.807(3)
1.35(2)
1.32(1)
1.353(9)
1.353(1)
1.354(1)
1.339d
1.357(5)
1.358(4)
1.360(4)
93(2)
94.2(4)
93.5(3)
93.0(1)
93.1(1)
87(20)
91(5)
91.0(3)
88.3(3)
This work
This work, rs
This work, rm (1)b
[19]
[24]
[16]
[17]
[18]
[20]
a
b
c
d
A
0
A0
A0
2 0
A
2 0
A
2 0
A
2 0
A
1
Structures are r0 unless indicated otherwise; errors are 3r.
For ca = 0.0274 and cc = 0.0108.
Structure refit using data from original reference.
Held fixed.
uniformly with increasing metal atomic radius. CuSH in
fact exhibits the shortest metal–sulfur bond length, and
copper has the correspondingly smallest atomic radius.
This correlation with atomic radii, as opposed to ionic
radii, is further evidence that the metal hydrosulfides
are at least partially covalent species.
The inertial defects calculated for CuSH and CuSD are
Do = 0.127 and 0.172 amu Å2, respectively, considering
both copper isotopomers, and are the smallest inertial defects found for the metal hydrosulfides. LiSH, the lightest
of these species, has Do = 0.194 amu Å2(LiSD:Do = 0.257
amu Å2), while BaSH, the heaviest known hydrosulfide,
exhibits Do = 0.239 and 0.323 amu Å2, for the main and
deuterated isotopomers [19,20]. This trend suggests that
CuSH is the most rigid of these species. Moreover, all
asymmetry components of CuSH and CuSD up to Ka =
8 fit to a classic asymmetric top pattern with few distortion
constants. In contrast, the Ka = 6 and 7 components of
BaSD, for instance, were perturbed from the normal pattern due to strong vibration–rotation coupling [20].
CuOH also exhibits some perturbations in its higher
Ka components [12]. Beyond Ka = 4, each additional Ka
transition required an extra centrifugal distortion parameter to fit the data. This effect is attributed to quasilinear
behavior. CuSH does not display such properties. While
there are significant variations in metal hydroxide geometries, the metal hydrosulfides studied thus far appear to
exhibit uniformly bent structures. These studies demonstrate that metal oxide and metal sulfide bonds display
quite different behavior, even for the simplest systems.
Acknowledgement
This research is supported by NSF Grant CHE-0411551.
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