The pure rotational spectrum of the CrS radical in its X5r state
R. L. Pulliam and L. M. Ziurys
Citation: J. Chem. Phys. 133, 174313 (2010); doi: 10.1063/1.3501354
View online: http://dx.doi.org/10.1063/1.3501354
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Published by the American Institute of Physics.
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THE JOURNAL OF CHEMICAL PHYSICS 133, 174313 共2010兲
The pure rotational spectrum of the CrS radical in its X 5⌸r state
R. L. Pulliam and L. M. Ziurysa兲
Department of Chemistry and Department of Astronomy, Steward Observatory, University of Arizona,
933 N. Cherry Ave., Tucson, Arizona 85721, USA
共Received 12 June 2010; accepted 23 September 2010; published online 3 November 2010兲
The pure rotational spectrum of the CrS radical has been measured in its ground X 5⌸r state using
gas-phase millimeter/submillimeter direct absorption methods. The molecule was created by the
reaction of chromium vapor, sublimed in a Broida-type oven, with hydrogen sulfide. Eleven
rotational transitions were recorded for this free radical in the frequency range of 280–405 GHz; in
most transitions, all five spin components were observed, and lambda-doubling was resolved in the
⍀ = 0, 1, and 2 ladders. The data were fit with a Hund’s case 共a兲 Hamiltonian and rotational,
spin-orbit, spin-spin, and lambda-doubling constants were established. Higher order spin and
spin-orbit terms were essential in the analysis. The lambda-doubling constants indicate a nearby 5⌺+
state at an energy of ⬃1500– 2000 cm−1. A bond length of 2.0781 Å was derived for CrS from the
data, which is larger than the value of 2.0682 Å found for MnS by ⬃0.01 Å. In contrast, the bond
distance for MnO is greater than that of CrO by 0.03 Å, an illustration of the subtle differences
between 3d oxide and sulfides. CrS is the second molecule in a 5⌸ state that has been studied by
rotational spectroscopy. © 2010 American Institute of Physics. 关doi:10.1063/1.3501354兴
I. INTRODUCTION
Transition metal sulfides have been known for many
years to have a wide range of applications. CdS, for example,
is an important paint pigment in “cadmium yellow”1 while
ZnS is a versatile semiconductor material;2 the latter is also
used for lenses and other optical devices in the infrared.3
Thin solid films of various metal sulfides 共copper, lead, mercury, and silver兲 have been used as microwave shields or
solar control coatings as well 共e.g., Ref. 4兲. In materials science, transition metal sulfides are used extensively as solid
lubricants,5 and are also known causes of mechanical defects
in metal alloys such as steel.6,7
In addition to their more mundane uses, transition metal
sulfide compounds play a role in astrophysics and astrobiology. Pyrite 共FeS2兲 may have acted as a catalyst that promoted
metabolism in primitive living systems on early Earth.8 Iron
sulfide features have also been detected in the solid state in
the midinfrared region around various carbon-rich planetary
nebulae,9 where they indicate the presence of FeS grains.
Furthermore, there is some evidence for the presence of gasphase TiS 共Ref. 10兲 and ZrS11,12 in the photospheres of
S-type Mira variable stars.
One interesting 3d sulfide is CrS. This species was first
studied in 1938 by Haraldsen et al.,13 who investigated its
magnetic properties in the solid state. Further work demonstrated that CrS and Cr2S3 exhibit electrical properties attributable to semiconductors,14 while the Cr7S8 is more metallic
in nature.15 The specific catalytic properties of chromium
sulfides are also of importance. Recent results show that
chromium sulfide catalysts increase the efficiency and deTelephone: 共520兲 621-6525. Fax: 共520兲 621-5554. Electronic mail:
[email protected].
a兲
0021-9606/2010/133共17兲/174313/6/$30.00
crease the cost of the hydrodesulfurization process, and
hence impact research into clean fuels.16 Yet, little is known
about the CrS monomer in the gas phase.
Numerous spectroscopic studies have been devoted to
CrO, the oxygen analog of CrS. Merer and co-workers,17–19
for example, measured the A 5⌺ − X 5⌸, A⬘ 5⌬ − X 5⌸, and
B 5⌸ − X 5⌸ electronic transitions of chromium oxide, resolving rotational structure and producing spectroscopic constants for the various states. More recently, the pure rotational spectrum of CrO has been recorded in all five spin
components by Sheridan et al.20 In contrast, only one investigation has been conducted for CrS. In 2001, Shi et al.21
studied the high resolution fluorescence spectrum of the
B 5⌸−1 − X 5⌸−1 band of chromium sulfide between 625 and
825 nm. The molecule was produced in a free jet expansion
by the reaction of ablated chromium and carbon disulfide
gas, and the spectra of 52CrS and 53CrS were both recorded.
Only the ⍀ = −1 spin component was observed in these data
out of the possible five, but lambda-doublets were resolved
at high J values in the P, Q, and R branches. Through ab
initio calculations, the authors deduced that the ground state
of CrS is 5⌸ with the corresponding 11␴11␦25␲1 electronic
configuration. They also reported a theoretical bond length in
the range of 2.065–2.103 Å for the ground state, which was
found to be in good agreement with the derived experimental
value of 2.071 Å for the ⍀ = −1 component.21
In this work we present the first measurement of the pure
rotational spectrum of CrS in its 5⌸r ground state. CrS is the
second molecule in a 5⌸ studied using rotational spectroscopy, the first being CrO.20 The data were recorded using
millimeter direct absorption methods in the frequency range
of 281–405 GHz. All five spin-orbit components were observed and lambda-doubling was resolved in the ⍀ = 0, 1,
and 2 lines. In this paper, we describe our measurements and
133, 174313-1
© 2010 American Institute of Physics
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174313-2
J. Chem. Phys. 133, 174313 共2010兲
R. L. Pulliam and L. M. Ziurys
analysis as well as an interpretation of the lambda-doubling
constants and their implications for the excited state manifold in CrS.
5
= -1
CrS (X r)
=0
J = 25
=1
II. EXPERIMENTAL
The pure rotational spectrum of CrS was measured using
one of the millimeter/submillimeter direct absorption spectrometers in the Ziurys group; see Ref. 22. The instrument
consists of a water-cooled steel reaction chamber which contains a Broida-type oven. The radiation source, which operates in the 65–850 GHz range, employs combinations of
Gunn oscillators with varacter multipliers. The radiation is
directed through the reaction chamber and back in a doublepass scheme using a combination of offset ellipsoidal mirrors
and a rooftop reflector, and then into the detector by means
of a polarizing grid. The detector, an InSb bolometer, is
cooled to 4 K with liquid helium. The radiation source is
FM-modulated and the signals from the detector are processed by a lock-in amplifier at 2f, allowing for phase sensitive detection.
CrS was created by the reaction of chromium vapor with
H2S in the presence of argon. Chromium pieces were sublimed in a Broida-type oven, which was run at 60 A and 10
V. To achieve the temperature required for sublimation, the
oven was partly wrapped in zirconia felt and packed with
alumina pieces. About 1–2 mTorr of H2S was added over the
top of the oven to produce CrS, while 15 mTorr of argon
carrier gas was introduced through the bottom of the oven.
Unlike most of our experiments, no dc discharge was required. Chromium production was monitored by initially
looking at transitions of CrO using N2O as the precursor.
Transition frequency measurements were obtained by
signal averaging between 2 and 6 scans, each 5 MHz in
width. The scans were averaged in pairs with equal numbers
in increasing and decreasing frequencies. Gaussian curves
were fit to the data to determine the center frequency. Line
widths averaged between 0.7 and 1.2 MHz over the range of
280–420 GHz.
III. RESULTS
An initial search for CrS was conducted by scanning
continuously over the 330–400 GHz range, guided by the
constants determined for the ⍀ = −1 spin component from
Shi et al.21 The ⍀ = 0, 1, 2, and 3 spin-orbit components were
readily identified in several rotational transitions in the
course of this search. The ⍀ = −1 pattern, however, was more
difficult to locate, as it was expected to consist of lambdadoublets, as found by Shi et al. It was then recognized that
these doublets were slowly crossing at the rotational transitions recorded. The ⍀ = −1 component was subsequently
identified as broader lines that consisted of unresolved doublets.
Figure 1 shows the fine structure pattern identified for
CrS, as found for the J = 25← 24 transition. The ordering of
the spin components is typical of a regular 5⌸ state, with the
⍀ = −1 component lying lowest in frequency with the greatest intensity. Lambda-doubling is largest in the ⍀ = 0 component and steadily decreases until it is not observable in the
293
294
295
296
Frequency (GHz)
24
=3
=2
297
298
FIG. 1. Stick spectrum of the J = 25← 24 transition of CrS centered around
295 GHz. All five spin components are shown, and lambda-doubling is
evident in the ⍀ = 0, 1, and 2 lines. The ⍀ = 2 component appears to be
shifted relative to the others, indicating perturbations by nearby excited
states.
⍀ = 3 lines. For example, at the J = 25← 24 transition, the
splitting is ⬃650 MHz for the ⍀ = 0 sublevel, decreasing to
⬃470 MHz for ⍀ = 1, then falling to ⬃20 MHz for the ⍀
= 2 ladder. The relative spacing between the centroids of the
spin components is not regular, however, in contrast to what
has been found for CrO.20 The ⍀ = 2 component appears to
be shifted to lower frequency relative to the ⍀ = 1 and 3
lines, suggestive of perturbations by nearby excited states.
A total of 11 rotational transitions were recorded for the
main isotopologue of CrS, as shown in Table I. All five spinorbit components were measured in 8 of the 11 transitions,
including the lambda-doublets for the ⍀ = 0, 1, and 2 ladders.
The e and f parity labeling of the doublets assumes that the
main perturber is a 5⌺+ excited state, as has been found for
CrO.17 As expected, the splitting in these three spin components increases with increasing J. The splitting in the
⍀ = −1 ladder begins at zero at the lowest J values, initially
increases with J, and then decreases. Eventually the doublets
will cross, as seen in our data. The two frequencies of the
doublets in this case were estimated from fits to the line
profiles, when possible, and these numbers are given in the
table.
Typical spectra from all five spin-orbit components are
shown in Fig. 2. In order to display both lambda-doublets of
the ⍀ = 0 and 1 ladders, a frequency break was inserted into
the data. The lambda-doublets are labeled by e and f for the
cases where they were resolved. The small intensity differences between the doublets are a result of slight variations in
production.
IV. ANALYSIS
The data for CrS in its X 5⌸r state were analyzed using
an effective case 共a兲 Hamiltonian consisting of the following
interactions:
Ĥeff = Ĥrot + Ĥso + Ĥss + Ĥld .
共1兲
The Hamiltonian terms account for the molecular frame rotation, spin-orbit interaction, electron spin-spin coupling, and
lambda-doubling. Because of the high spin and orbital angu-
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174313-3
J. Chem. Phys. 133, 174313 共2010兲
Pure rotational spectrum of CrS
TABLE I. Submillimeter transition frequencies of CrS 共X 5⌸r兲.a
J+1←J
⍀
Parity
24← 23
⫺1
⫺1
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
25← 24
26← 25
27← 26
28← 27
29← 28
30← 29
␯obs
a
281 054.135b
281 054.135b
283 583.770
284 036.216
284 638.543
284 623.798
285 951.232
285 951.232
292 749.141
292 749.141
293 969.688
294 621.185
295 847.374
295 375.336
296 459.419
296 476.858
297 842.290
297 842.290
304 442.120
304 442.120
306 385.969
305 703.343
307 163.901
307 655.675
308 312.103
308 293.215
309 730.582
309 730.582
316 133.116
316 133.116
317 434.144
318 148.375
319 460.885
318 949.403
320 123.524
320 145.196
321 615.856
321 615.856
327 821.033
327 822.033
329 908.310
329 161.930
330 731.709
331 263.012
331 974.680
331 950.960
333 498.020
333 498.020
339 508.667
339 508.667
340 886.567
341 665.689
343 061.753
342 510.897
343 774.999
343 801.502
345 376.959
345 376.959
351 193.056
351 193.056
␯obs − ␯calc
¯
¯
0.345
0.315
0.527
⫺0.596
⫺0.004
⫺0.119
⫺0.134
⫺0.305
0.304
⫺0.213
⫺0.171
0.208
⫺0.583
0.557
⫺0.049
⫺0.103
⫺0.130
⫺0.011
⫺0.116
0.106
0.050
0.001
0.467
⫺0.496
⫺0.094
0.092
0.055
⫺0.014
⫺0.009
⫺0.030
0.076
⫺0.072
⫺0.400
0.380
0.111
⫺0.116
0.143
0.120
0.045
⫺0.090
⫺0.170
0.166
0.243
⫺0.256
⫺0.143
0.130
0.134
0.152
⫺0.157
0.112
0.244
⫺0.247
⫺0.090
0.076
⫺0.179
0.148
0.147
0.198
TABLE I. 共Continued.兲
J+1←J
a
31← 30
32← 31
33← 32
34← 33
⍀
Parity
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
2
2
⫺1
⫺1
0
0
1
1
2
2
3
3
⫺1
⫺1
0
0
1
1
3
3
⫺1
⫺1
0
0
1
1
2
2
3
3
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
e
f
␯obs
␯obs − ␯calc
a
353 420.387
352 607.987
354 286.283
354 857.423
355 625.463
355 595.857
357 252.566
357 252.566
362 875.092
362 875.092
364 325.941
365 172.344
366 649.439
366 058.371
367 413.448
367 445.988
374 554.572
374 554.572
376 921.388
376 040.637
377 826.720
378 437.886
379 263.366
379 227.306
380 993.343
380 993.343
386 231.616
386 231.616
387 751.713
388 667.540
390 222.673
389 591.512
392 858.236
392 858.236
397 905.906
397 905.906
400 410.552
399 459.086
401 352.337
402 003.561
402 887.761b
402 844.666b
404 719.397
404 719.397
a
0.137
⫺0.163
⫺0.263
0.244
⫺0.127
0.127
⫺0.214
0.176
0.232
⫺0.357
⫺0.245
0.151
0.172
⫺0.197
0.402
⫺0.328
0.018
⫺0.083
0.070
⫺0.080
⫺0.166
0.056
⫺0.705
0.792
⫺0.269
0.276
⫺0.026
0.039
0.083
0.008
⫺0.089
0.132
0.305
⫺0.336
0.128
⫺0.041
⫺0.311
0.127
0.274
⫺0.399
¯
¯
⫺0.345
0.403
a
In MHz.
Not included in fit.
b
lar momentum of the state, higher order terms were necessary to achieve a good fit. The third order spin-orbit correction, characterized by the constant ␩ and its distortion
constant ␩D, for example, was needed for a successful
analysis,17
冉
共3兲
Ĥso
= ␩LzSz Sz2 −
+
␩D
2
3S2 − 1
5
再 冋
LzSz Sz2 −
冊
册
冎
3S2 − 1
共J − S兲2 .
5
共2兲
The fourth order spin term ␪ 共Ref. 18兲 and its centrifugal
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174313-4
J. Chem. Phys. 133, 174313 共2010兲
R. L. Pulliam and L. M. Ziurys
5
CrS (X r)
a)
J = 31
30
= -1
362855
362895
J = 32
31
=0
ef
376033
376048
J = 30
29
=1 f
e
354278
354293
J = 31
=2
30
e
367412
b)
fe
376916
376932
c)
fe
354851
354867
d)
f
367448
e)
J = 30
29
=3
357235
357270
Frequency (MHz)
FIG. 2. Millimeter spectra of CrS measured in this work, displaying data
共a兲–共e兲 for all five spin components. There is a frequency break in the
spectrum for the ⍀ = 0 and 1 data. Lambda-doublets, labeled by e and f
notation, are resolved in the ⍀ = 0, 1, and 2 features. Each spectrum was
obtained in a single 110 MHz wide scan, approximately 2 min in duration,
and then cropped to display the frequency ranges shown in the figure.
distortion ␪D were required as well, but it was necessary to
fix theta to the value found from the initial fit; otherwise, the
parameter was not defined. As discussed in Brown et al.,23
lambda-doubling in 5⌸ states requires three constants: o, p,
and q. All three effective fitting parameters q, p + 2q, and o
+ p + q were determined in the analysis. It was also necessary
to include the centrifugal distortion terms to all three
lambda-doubling constants.
The final fit to the data for CrS is presented in Table II.
Also given in the table for comparison is the rotational constant B and B 共⍀ = −1兲 from the optical work of Shi et al.21
The B value for the ⍀ = −1 spin component is smaller than
that found from the millimeter measurements by about 25
MHz: 5832.5 MHz versus 5859 MHz. Because these authors
only measured the ⍀ = −1 component of CrS, they estimated
the rotational constant from the relationship B共⍀ = −1兲 = B
+ 共2B 2⌺ / ⌳A兲. They also assumed that the spin-orbit constant
of CrS was equal to that of CrO 共A = 62.9 cm−1兲. It should be
noted that the millimeter fit indicates a spin-orbit constant of
about 95 cm−1, although, given the relatively high values of
␪ and ␩, this value may not be meaningful. As can be seen
from the table, their value for B ⬃ 5907 MHz compares reasonably well with the value of 5913 MHz obtained in this
work, but this result is somewhat fortuitous. Because at least
one spin component in CrS appears to be perturbed, the relationship between B and B共⍀兲 is distorted. The rms of the fit
was 263 kHz.
V. DISCUSSION
All five spin components have been identified in CrS for
the first time, confirming the 5⌸r assignment of the ground
state. Chromium sulfide is the second molecule in a 5⌸
ground state to be studied at high spectral resolution, therefore providing at some level a test of angular momentum
coupling theory. The higher order fine structure terms ␪, ␪D,
␩, and ␩D were found to be necessary for accurate modeling
of the spectral data. As discussed by Barnes et al.,18 ␪ is
pertinent to states of quintet multiplicity and higher, as found
for CrS. The parameter ␩ characterizes states with angular
momentum of quartet and higher multiplicity.23
The presence of lambda-doubling in the ⍀ = 0, 1, and 2
ladders suggests the existence of a nearby excited 5⌺+ state,
as found for CrO.17–20 Based on ab initio multireference calculations, Shi et al. predicted the ordering of the molecular
orbitals in CrS. To produce a 5⌸ ground state, these authors
proposed the electron configuration of 共core兲 11␴11␦25␲1.
The 11␴ orbital arises principally from the 4s orbital on the
chromium atom, while the 1␦ and 5␲ orbitals are chiefly 3d
in character; see Fig. 3. The promotion of the 5␲ electron
into the orbital directly above in energy, the 12␴ orbital, will
create a low-lying 5⌺+ state. As predicted by Shi et al., this
sigma orbital also is 3d in character. Therefore, the X 5⌸ and
the 共presumably A兲 5⌺+ states function as a d␲ / d␴ pair, and
pure precession can be assumed.24
To a first approximation, lambda-doubling in CrS arises
from the second order mixing of the ground 5⌸r state with
the excited 5⌺+ state through spin-orbit and rotational interactions. The lambda-doubling constant q results from the rotational coupling,23,24 i.e.,
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174313-5
J. Chem. Phys. 133, 174313 共2010兲
Pure rotational spectrum of CrS
TABLE II. Spectroscopic constants in MHz for CrS 共X 5⌸r兲. 共Values in parenthesis are 3␴ error.兲
Parameter
This work
Opticala
This work 共 5⌸−1兲
B
D
A
AD
AH
共o + p + q兲
共p + 2q兲
q
共o + p + q兲D
共p + 2q兲D
qD
␭
␭D
␭H
5913.3568共77兲
0.004 349 6共44兲
2 854 000共122 000兲
0.456共99兲
⫺0.000 178共10兲
417.3共7.2兲
761共62兲
⫺9.94共54兲
1.166共81兲
0.0318共13兲
0.001 090共28兲
⫺9333共250兲
⫺1.078共60兲
0.000 084 9共14兲
6730共740兲
1.77共32兲
753.195b
0.4037共80兲
0.263
5906.8共3兲
5859.0005共171兲
0.003 213 6共103兲
␩
␩D
␪
␪D
rms
Optical 共 5⌸−1兲
a
5832.5共3兲
0.145
a
Reference 21.
Held fixed.
b
qv ⬵ 4
兺 兺 共− 1兲s
n⬘,⌳⬘ v⬘
兩具n,⌳ = 1兩BT11共L兲兩n⬘,⌳ = 0典兩2
.
En,⌸ − En⬘,⌺
共3兲
Here T11共L兲 = ⫿ 1 / 2−1/2L⫾, and the matrix element above reduces to
具 ⌸兩L+兩 ⌺典 = 关l共l + 1兲兴1/2 .
5
共4兲
5
In this case l = 2, and the entire expression for qv becomes
4
pv ⬵ −
兺
关S共S + 1兲共2S + 1兲兴1/2 n ,⌳
qv ⬵
12B2
.
E⌸ − E⌺
共5兲
Using the value of q as determined in the fit, the above
equation suggests E⌺ ⬃ 1410 cm−1.
The constant p involves both spin-orbit and rotational
terms,23
1
兩具n,⌳ = 1兩BT11共L兲兩n⬘,⌳ = 0典兩 ⫻ 兺 j兩具n⬘,⌳ = 0兩T−1
共a jl j兲兩n,⌳ = 1典兩具S兩兩T1共s j兲兩兩S典
. 共6兲
兺 共− 1兲
En,⌸ − En⬘,⌺
v
s
⬘ ⬘ ⬘
Again, making the simple assumption that there is a unique
5 +
⌺ perturbing state, the expression for pv reduces to
pv ⬵
3AB
.
E⌸ − E⌺
共7兲
Using the values of A, B, and p from the CrS fit, the suggested energy difference is E⌺ − E⌸ ⬃ 2160 cm−1. Therefore,
the lambda-doubling constants overall indicate a 5⌺+ state
lying ⬃1400– 2100 cm−1 above the ground state.
Unfortunately, little is known about the excited state
manifold in CrS from experimental work outside the study
by Shi et al. They located an excited 5⌸ state at
⬃13 963 cm−1 above the ground state. In comparison,
Merer and co-workers found the A 5⌺+, A⬘ 5⌬, and B 5⌸
excited states in CrO to lie at ⬃8100, 11 900, and
16 580 cm−1 above the ground 5⌸ state. By analogy, these
results would suggest that the energy estimate for the 5⌺+
state of ⬃1500– 2000 cm−1 is probably not far from the true
value.
Based on their estimate of the rotational constant, extrapolated from the ⍀ = −1 data, Shi et al. determined a Cr–S
bond length of r0 = 2.0713 Å. Our results, based on all five
spin ladders, indicate r0 = 2.0781 Å, in relatively close agreement. Theoretical calculations by Shi et al. and Bridgeman
and Rothery25 predict the bond length to be in the range of
2.065–2.080 Å,21,25,26 which agrees with our experimental
value. Based on pure rotational spectroscopy, MnS has been
found to have a bond length of r0 = 2.0682 Å.27 Thus, the
bond length decreases in the sulfides from chromium to manganese. In contrast, this quantity increases from 1.6213 to
1.648 Å going from CrO to MnO.20,28 Thus, while 3d sulfides are similar to the 3d oxides, there are subtle differences
between the two classes of compounds. As discussed by
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174313-6
J. Chem. Phys. 133, 174313 共2010兲
R. L. Pulliam and L. M. Ziurys
1
12
5
3d
CrS (X5r)
1
4s
11
Cr
4
3p
S
10
FIG. 3. A molecular orbital diagram for CrS based on ab initio calculations
of Shi et al. 共Ref. 21兲. The 5⌸ ground state arises from a 11␴11␦25␲1
electron configuration, as shown in the diagram. A nearby excited 5⌺ state
arises from the promotion of the 5␲ electron to the 12␴ orbital, as shown in
grey scale in the figure.
Zack and Ziurys,29 such variations likely result from better
orbital overlap of the 3d metals with sulfur 3p orbitals than
with the oxygen 2p. Hence, the “double hump” structure
exhibited by the bond distances of the oxides across the periodic table25 is only qualitatively duplicated in the 3d sulfides.
VI. CONCLUSIONS
Determination of the properties of the 3d sulfides will
further the understanding of bonding in transition metal compounds. This work has clearly established the ground state of
CrS as 5⌸r, and has provided accurate rotational, fine structure, and lambda-doubling constants for this free radical. The
spectrum of CrS suggests a nearby 5⌺ excited state, lying
⬃1500– 2000 cm−1 higher in energy. Additional electronic
spectroscopy of CrS is needed to further characterize its excited state manifold.
ACKNOWLEDGMENTS
This work is supported by NSF Grant No. CHE-0718699.
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