First observation and electronic spectroscopy of chromium mononitride: The a 4Πr←X 4Σ- transition near 745 nm

Article abstract of DOI:10.1063/1.473485

We report the first gas phase spectroscopic study of chromium mononitride. CrN molecules were generated in our laser vaporization molecular beam source and studied using laser induced fluorescence techniques. Twelve vibronic subbands of Cr¹⁴N have been rotationally analyzed in the 745-647 nm region. These bands are assigned to the A ⁴Π_r←X ⁴Σ^- transition. The assigned ground state electron configuration 1 δ²9σ¹ and symmetry are identical to those of the isovalent VO, MoN, and WN molecules. The energy observed for the excited ⁴Π_r state matches closely the first ⁴Π state energy derived from a recent ab initio calculation [J. F. Harrison, J. Phys. Chem. 100, 3513 (1996)]. In addition to the A-X transition, 11 other bands of Cr¹⁴N have been identified and vibrationally assigned to transitions involving two other excited states, presumably the B⁴Σ^-, and a ²Π state. Comparisons with the isovalent VO, MoN, and WN systems have provided more insights into the bonding and electronic structure of the CrN molecule.

Full text of DOI:10.1063/1.473485

First observation and electronic spectroscopy of chromium mononitride: The A4Πr←X
4Σ− transition near 745 nm
Walter J. Balfour, Charles X. W. Qian, and Chi Zhou
Citation: The Journal of Chemical Physics 106, 4383 (1997); doi: 10.1063/1.473485
View online: http://dx.doi.org/10.1063/1.473485
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/106/11?ver=pdfcov
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First observation and electronic spectroscopy of chromium mononitride:
4
4
The A ⌸r—X ⌺؊ transition near 745 nm
Walter J. Balfour, Charles X. W. Qian, and Chi Zhoua)
Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, British Columbia,
Canada V8W 3V6
͑Received 4 November 1996; accepted 12 December 1996͒
We report the first gas phase spectroscopic study of chromium mononitride. CrN molecules were
generated in our laser vaporization molecular beam source and studied using laser induced
fluorescence techniques. Twelve vibronic subbands of Cr14N have been rotationally analyzed in the
4
4
745–647 nm region. These bands are assigned to the A ⌸r←X ⌺Ϫ transition. The assigned
ground state electron configuration 1␦29␴1 and symmetry are identical to those of the isovalent VO,
4
MoN, and WN molecules. The energy observed for the excited ⌸r state matches closely the first
4⌸ state energy derived from a recent ab initio calculation ͓J. F. Harrison, J. Phys. Chem. 100, 3513
͑1996͔͒. In addition to the A-X transition, 11 other bands of Cr14N have been identified and
vibrationally assigned to transitions involving two other excited states, presumably the B4⌺Ϫ, and
a 2⌸ state. Comparisons with the isovalent VO, MoN, and WN systems have provided more insights
into the bonding and electronic structure of the CrN molecule. © 1997 American Institute of
Physics. ͓S0021-9606͑97͒01911-9͔
INTRODUCTION
lecular beam source, two pulsed laser systems, and the nec-
essary hardware and software for LIF detection.
Gas phase spectroscopic studies of transition metal ni-
trides can provide crucial information about the bonding be-
tween a transition metal atom and a nitrogen atom and have
attracted a significant amount of interest among experimen-
talists and theorists alike.1–40 In contrast to metal oxides and
hydrides where many detailed studies exist,41,42 gas phase
studies of metal nitrides are rather limited. To our knowl-
edge, currently only 11 metal nitrides ͑ScN,1 TiN,2–8 VN,9–11
YN,12 ZrN,13,14 NbN,15–20 MoN,21–25 WN,26 ReN,27 IrN,28
and PtN29,30͒ have published gas phase spectra. Ab initio cal-
culations involving these molecules are also limited. Publi-
cations have appeared on ScN,31 TiN,32,33,35 VN,34,35
CrN,35,36 FeN,36 YN,37 NbN,38 MoN,39 and PtN40 molecules.
In this paper, we detail the first spectroscopic character-
ization of the 3d metal nitride, chromium mononitride
͑CrN͒. LIF spectra of Cr14N and Cr15N have been recorded
in the 370–745 nm region and rotational analyses have been
carried out for 12 of the observed Cr14N vibronic subbands.
Electron configurations for both the ground and the excited
states have been assigned based on the ab initio
calculations35,36 and by comparison with the isovalent VO,41
MoN,21–25 and WN26 molecules. Experimental observations
agree well with the ab initio results and point to the locations
of several other excited states not included in the calculation.
A homemade pulsed molecular beam valve ͑pulse width
ϭ200 ␮s, 0.5 mm diameter͒ was used44 with a rotating chro-
mium rod ͑5 mm diameter and 3 cm long͒ mounted close to
the opening of the nozzle. The carrier gas ͑2% ammonia in 1
atm helium͒ was then expanded through an attached 17 mm
long ͑2 mm diameter͒ channel into a high vacuum chamber.
The vacuum chamber, a 30 cm black anodized cubic alumi-
num one, was pumped by a 16 cm diffusion pump ͑Edwards
diffstack 160͒. Ion gauge readings of 1ϫ10Ϫ4
and 1ϫ10Ϫ5
Torr are typical with the molecular beam switched on and
off, respectively.
The second harmonic ͑532 nm͒ output of a Nd:YAG
laser ͑Continuum NY60͒ was used as the vaporization source
whereas a Nd:YAG pumped tunable dye laser ͑Lumonics
HY600 and HD300͒ was used to excite the jet-cooled CrN
molecules. A 0.2 cmϪ1 resolution was typical in the 370–745
nm region and several dyes ͑e.g., DCM, LDS 698, and LDS
751͒ were used. The LIF detection system consists of a col-
lection lens ͑50 mm diameter and fϭ75 mm͒, a Jobin Yvon
H20 monochromator ͑used as a band pass filter͒ and a pho-
tomultiplier tube ͑PMT; Hamamatsu R106UH͒. The signal
from the PMT was collected on a digital oscilloscope ͑Tek-
tronix 2440͒ and transferred to a 386 computer. To record a
LIF spectrum, the dye laser wavelength was scanned with a
step size of 0.001 nm and for each wavelength setting, the
signal was averaged for 10 laser shots.
EXPERIMENTAL METHOD
To confirm the identity of the carrier and to establish
vibrational assignments in the spectrum, 15NH3 ͑99%, Cam-
bridge Isotope͒ was used to obtain the LIF spectrum of
Cr15N. The wavelength calibration was carried out using the
observed Cr atomic LIF lines in this region.45 The absolute
wave numbers reported here are believed to be accurate
within 2 cmϪ1 and the relative positions should be precise
The experimental apparatus used to produce CrN has
been described previously43 and only a brief outline is given
here. The setup consists of a typical laser vaporization mo-
a͒
Permanent address: Institute of Opto-electronics, Harbin Institute of Tech-
nology, Harbin, 150001, P.R. China.
J. Chem. Phys. 106 (11), 15 March 1997
0021-9606/97/106(11)/4383/6/$10.00
© 1997 American Institute of Physics
4383
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4384
Balfour, Qian, and Zhou: Electronic spectroscopy of CrN
within 0.1 cmϪ1. To avoid power broadening and saturation,
the amplifier of the dye laser was normally removed during
our experiment. For several weak subbands ͑e.g., bands at
647.1, 650.3, 653.4, and 656.0 nm͒, however, the amplified
dye laser output was used to obtain satisfactory signals.
RESULTS AND ANALYSES
A. The rovibrational analysis of the A-X system
Ab initio calculations35 and comparison with the isova-
lent MoN21–25 and WN26 systems indicate with little doubt
4
4
that the first optical transition should be the A ⌸r←X ⌺Ϫ
system. The observation of three groups of four subbands,
each separated by about 910 cmϪ1, and with an origin around
739 nm, immediately suggested the discovery of this ex-
pected transition. Isotope shifts of the Cr15N bands con-
firmed the carrier to be CrN and established the vibrational
assignment. The three groups centered around 651.5, 692.5,
and 739.2 nm are therefore confidently assigned to the ͑2-0͒,
4
4
͑1-0͒, and ͑0-0͒ bands of the A ⌸r←X ⌺Ϫ system. Within
each of the three bands, there are four subbands correspond-
ing to transitions to the four ⍀ sublevels of the upper ⌸r
4
manifold. The nearly equal spacing between the subbands
46
suggests that we have a Hund’s case ͑a͒ ͓or case ͑ab͔͒ 4⌸r
state with only small perturbations from another state ͑most
likely, a ⌸ state, as in VO41͒.
2
Due to the complexity of the ⌸r← ⌺Ϫ transition and
our limited laser resolution, a simulation program written for
RhO analysis was modified to fit the CrN system. In fact,
two programs were created for each of the four subbands,
one being used to simulate the spectrum, the other to perform
the least squares analysis. These programs proved to be valu-
able since branch patterns are frequently unusual for CrN.
As displayed in Fig. 1, each of the 4 subbands consists
of 12 branches with line spacing of about ϩ5BЈ ͑one
branch͒, ϩ3BЈ ͑two branches͒, ϩBЈ ͑three branches͒, ϪBЈ
͑three branches͒, Ϫ3BЈ ͑two branches͒, and Ϫ5BЈ ͑one
branch͒. The analyses were carried out in an iterative ap-
proach; the two branches with 5BЈ separation were first used
in the least squares fit to obtain an initial fit. The output of
the simulation program using the obtained fitting parameters
then helped to identify other branches. Transitions from
these branches were added to the least squares fit. Typically
about 100 lines were used for each subband in the least
squares fit with NЉ up to 20. The root mean square deviation
4
4
4
Ϫ
FIG. 1. ͑A͒ and ͑B͒: sections of the LIF spectrum of the A 4⌸r←X
͑2-0͒ transition of Cr14N.
⌺
of the ⍀ϭ1/2 and Ϫ1/2 subbands are shifted to the blue by
about 9 cmϪ1 and 28 cmϪ1, respectively, from values pre-
dicted using these constants. These shifts are most likely
2
related to the perturbation caused by a ⌸ state located at
higher energy. We proceeded by using the following case ͑a͒
effective Hamiltonian with individually adjustable T⍀ val-
ues:
2
F J ͒ϭT ϩBJ J ϩ1͒ϪD J J ϩ1͒
͔
͑
͑
Ј Ј
͓ ͑
Ј Ј
Ј
⍀
Ϯq J ϩ1/2͒/2Ϯ Ϫ1/2͒p J ϩ1/2͒3.
͑1͒
͑
͑
͑
Ј
j
Ј
is about 0.07 cmϪ1 for a majority of the 12 subbands with the
This energy expression has been used by several groups21,26
4
v
Јϭ1 and
in their analyses of ⌸r← ⌺Ϫ transitions. The results of this
analysis are listed in Table I and Table II. Several weak
features cannot be assigned to 52Cr14N: it is likely that they
are due to the less abundant 53Cr14N isotopomer.
4
4
exceptions of 2 subbands involving the
⌸
3/2
ϭ0 excited states. Careful examination of the deviations
vЈ
suggests that the high J levels of these particular excited
states are perturbed in a way that cannot be described by the
effective Hamiltonians used in our simulation and fitting pro-
grams.
B. Vibrational assignments of the other excited states
The ⍀ϭ5/2 and 3/2 subbands of the ͑2-0͒ transition
were first analyzed together using case ͑ab͒ formulas47 for
the upper state and the known Hamiltonian matrix elements
Two additional systems, with their ͑0-0͒ bands located
near 488.0 and 488.5 nm ͓systems ͑II͒ and ͑III͔͒, are also
observed in this study. The strong transition ͑II͒ with its
origin near 488 nm is assigned to the case ͑a͒ allowed
4
for a ⌺Ϫ state.48 This analysis yielded the origin of the
ϭ2 state and the spin-orbit coupling constant. ͑These con-
vЈ
stants are included in Table II.͒ It is apparent that the centers
B ⌺Ϫ←X ⌺Ϫ transition. Another much weaker system
4
4
J. Chem. Phys., Vol. 106, No. 11, 15 March 1997
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Balfour, Qian, and Zhou: Electronic spectroscopy of CrN
TABLE I. Table of assigned lines of the CrN A-X ͑2,0͒ band ͑values in cmϪ1͒.
4385
4
4
A
N
⌸
(5/2)←X
uR41
⌺
Ϫ(2,0)
tR42
sR43
rR44
tQ41
rQ43
qQ44
rP42
qP43
pP44
Љ
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
15 460.72
463.54
466.39
469.21
472.06
474.88
477.69
480.49
483.20
485.93
488.62
491.26
15 456.03
456.89
458.14
459.52
460.93
462.41
463.92
465.40
466.91
468.35
469.86
471.27
15 459.28
460.86
462.41
464.14
465.72
467.32
468.87
470.41
472.06
473.42
15 449.58
450.32
450.94
451.49
451.99
452.47
15 446.03
445.45
444.79
444.02
443.28
442.50
441.64
440.75
439.85
438.87
15 447.29
446.29
445.36
444.38
443.45
442.50
441.54
440.52
439.47
438.66
437.75
15 443.74
442.04
440.23
438.32
436.32
434.25
432.15
430.04
427.86
425.65
423.32
15 439.30
437.34
435.37
433.34
431.27
429.15
427.03
424.82
422.67
420.46
418.08
15 439.43
436.53
433.51
430.39
427.12
423.91
420.56
417.23
15 448.80
448.22
447.46
446.69
445.86
445.05
444.02
443.28
442.40
441.18
440.23
4
4
A
N
⌸
(3/2)←X
⌺
Ϫ(2,0)
tR31
sR32
rR33
qR34
sQ31
qQ33
pQ34
qP32
pP33
oP34
Љ
0
1
2
3
4
5
6
7
15 381.03
383.80
386.59
389.39
392.11
394.84
397.54
400.15
402.81
405.37
407.89
410.38
412.81
415.21
15 375.85
376.32
377.20
378.33
379.59
381.03
382.38
383.80
385.15
386.59
387.76
389.08
390.10
391.47
392.83
15 378.03
379.59
381.17
382.74
384.25
385.77
387.40
388.68
390.10
391.47
392.83
394.08
395.31
396.59
397.54
398.94
15 369.92
370.60
371.15
371.62
372.02
372.40
15 368.90
369.63
369.73
369.45
368.90
368.19
367.46
366.52
365.48
364.41
363.33
362.19
360.97
359.76
358.35
356.84
355.54
354.10
352.66
15 366.89
366.40
365.69
364.98
364.20
363.33
362.29
361.46
360.38
15 366.52
365.48
364.01
362.19
360.38
358.28
356.25
354.10
351.91
349.60
347.27
344.93
342.44
339.85
337.35
15 368.59
367.46
366.52
365.48
364.20
363.33
362.29
360.97
360.02
358.87
357.57
356.25
354.95
353.72
15 361.46
359.55
357.57
355.42
353.39
15 359.76
356.84
353.72
350.54
347.27
343.87
340.46
337.00
8
9
10
11
12
13
14
15
16
17
18
19
20
4
4
A
N
⌸
(1/2)←X
⌺
Ϫ(2,0)
sR21
rR22
qR23
pR24
rQ21
pQ23
oQ24
pP22
oP23
nP24
Љ
0
1
2
3
4
5
6
7
8
15 311.12
313.86
316.54
319.12
321.72
324.24
326.70
329.17
331.52
333.85
336.08
338.25
340.44
342.44
15 296.36
297.13
297.79
298.25
298.67
299.07
15 306.62
308.14
309.52
311.12
312.52
313.86
315.08
316.25
317.43
318.53
319.56
320.55
321.25
15 296.36
296.80
296.71
296.36
295.75
294.84
293.88
292.82
291.72
290.49
15 294.13
293.46
292.78
291.91
291.07
289.97
288.94
287.84
286.58
285.37
15 297.13
295.75
294.58
293.46
292.29
291.14
289.88
288.75
287.42
285.97
15 293.95
292.78
291.23
289.43
287.45
285.41
283.17
280.81
278.50
15 290.65
288.78
286.88
284.76
282.61
280.39
278.12
15 306.36
307.55
308.80
310.18
311.30
15 289.74
286.95
283.94
280.74
277.35
273.97
9
299.52
299.52
10
11
12
13
14
J. Chem. Phys., Vol. 106, No. 11, 15 March 1997
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4386
Balfour, Qian, and Zhou: Electronic spectroscopy of CrN
TABLE I. ͑Continued.͒
4
4
A
⌸
(Ϫ1/2)←X
rR11
⌺
Ϫ(2,0)
N
qR12
oR14
qQ11
oQ13
nQ14
pP11
oP12
nP13
mP14
Љ
0
1
2
3
4
5
6
7
8
9
15 242.90
245.53
248.09
250.53
252.95
255.39
257.70
259.93
262.08
264.01
266.06
267.95
15 241.55
243.00
244.37
245.72
246.97
248.09
249.16
250.23
251.13
252.00
15 239.95
241.07
242.18
243.27
244.27
245.20
246.09
246.97
15 231.64
231.59
231.11
230.41
229.41
228.37
227.07
225.75
224.38
222.83
221.25
219.44
15 228.37
227.51
226.70
225.65
224.52
223.36
221.97
220.65
15 230.64
229.34
15 227.30
225.65
223.71
221.60
219.35
216.87
214.32
211.66
15 223.24
221.37
219.09
216.73
214.32
211.85
209.25
228.21
15 221.83
218.70
215.43
212.01
208.44
226.95
224.29
222.83
10
11
12
13
14
15 237.28
236.68
235.96
DISCUSSION
͑III͒, very close to system ͑II͒, seems to be related to system
͑II͒. The appearance of the vibronic bands within each sys-
tem ͑i.e., II and III͒ changes substantially with the vibra-
tional quanta suggesting that these two systems share a com-
mon ͑ground͒ state and that their excited states are strongly
interacting.
Very weak ͑0-1͒ bands have been observed for these two
systems and suggest that all share a common ground state.
The vibrational assignments are obtained solely from the ob-
served 14N–15N isotope shifts. Due to the weak intensities of
some bands and perturbations appearing in the stronger
bands, rotational analyses are not completed for these sys-
tems and will be the subject of a future study.49
A. Molecular orbitals and electronic configurations
Recently, Harrison35 has carried out a detailed ab initio
calculation which established the symmetries, bond lengths,
and energies of the ground and first excited quartet state of
CrN. Here we discuss the molecular orbital ͑MO͒ scheme to
provide a coherent picture both about the X and A states, and
other excited states not included in the ab initio calculation.
The MO scheme is also convenient for the comparison with
isovalent VO, MoN, and WN systems. An MO diagram be-
lieved to be appropriate for CrN is presented in Fig. 2. This
diagram is similar to the MO diagram used by Merer for
4
4
TABLE II. Spectroscopic constants for the A
A statea
⌸
and X ⌺Ϫ states ͑cmϪ1͒.
r
⍀
T
B
͑106͒ D
p
͑104͒ pj
Deviationb
Ј
ϭ0
—
—
—
vЈ
5/2
3/2
1/2
13 639.98 ͑9͒
13 559.61 ͑15͒
13 485.37 ͑5͒
13 419.52 ͑9͒
0.6216 ͑6͒
0.6123 ͑10͒
0.6040 ͑4͒
0.5924 ͑11͒
—
—
—
—
—
0.07
0.15
0.05
0.11
0.005 ͑30͒
0.042 ͑10͒
Ϫ0.035 ͑25͒
Ϫ1/2
2.0 ͑60͒
ϭ1
vЈ
5/2
3/2
1/2
14 553.48 ͑7͒
14 471.86 ͑15͒
14 397.44 ͑5͒
14 332.46 ͑8͒
0.6158 ͑8͒
0.6051 ͑8͒
0.5980 ͑5͒
0.5891 ͑9͒
—
12.0 ͑30͒
—
—
—
—
—
0.07
0.13
0.05
0.08
Ϫ0.001 ͑14͒
0.042 ͑13͒
Ϫ0.032 ͑20͒
Ϫ1/2
12.0 ͑60͒
1.4 ͑8͒
ϭ2
—
—
—
—
vЈ
5/2
3/2
1/2
15 454.56 ͑6͒
15 371.32 ͑8͒
15 297.45 ͑6͒
15 233.43 ͑7͒
0.6109 ͑6͒
0.6031 ͑6͒
0.5937 ͑6͒
0.5821 ͑8͒
—
—
—
—
—
0.06
0.08
0.06
0.06
Ϫ0.001 ͑20͒
0.042 ͑15͒
Ϫ0.038 ͑16͒
Ϫ1/2
X state: ϭ0; ␭ϭ2.628͑82͒, ␥ϭ0.005͑8͒, B ϭ0.6259͑8͒, rЉ ϭ 0.1563 nm.
vЉ
Љ
0
aAϭ83.067͑85͒, Tv ϭ2ϭ15 329.99͑9͒ and B
ϭ 0.5986(8) were obtained from a global fit of ͑ ϭ2͒. ⍀ ϭ5/2 and 3/2 subbands, see text for detail.
Ј
vЈ
Ј
Ј
Јϭ2
v
bThe deviation indicates two standard deviation.
J. Chem. Phys., Vol. 106, No. 11, 15 March 1997
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Balfour, Qian, and Zhou: Electronic spectroscopy of CrN
TABLE III. Vibronic band assignments of CrN.
4387
then given by A(4⌸,␦2␲)ϭa /3. If we assume that
␲
a ϭ␨(3d) then one obtains Aϭ81 cmϪ1 50
This value is
.
4
Ϫ
4
Ϫ
␲
B
⌺
←X
⌺
͑system II͒
System III
␭ ͑nm͒
very close to the observed 83 cmϪ1 but one must be cautious
about such an agreement, since ab initio calculations35 sug-
gest that the 4␲ orbital arises predominantly from Cr 4p
orbitals.
␭ ͑nm͒
Tv ͑cmϪ1
͒
Tv ͑cmϪ1
͒
vЈ
vЈ
Ј
Ј
0a
1
2
488.0
473.0
459.2
446.1
433.7
422.2
411.2
20 486
21 136
21 773
22 410
23 051
23 682
24 313
0
0
1
1
2
2
488.5
482.0
466.3
20 465
20 741
21 439
3a
4
447.0
441.3
22 365
22 654
B. Equilibrium constants and the bonding in the X
and A states
5a
6
With our CrN analysis, the A-X transitions for three
group VI A nitrides are now characterized.21–26 The A state
energy increases systematically as one moves down the
group, Cr, Mo, W. This can be viewed as evidence for the
changing nd-(nϩ1)p hybridization in the ␲ nonbonding or-
bitals. As was demonstrated sometime ago for MoN, the ␲
nonbonding orbital has a significant 5p contribution.39 The
present observation seems to indicate that this d-p hybrid-
ization is even more important for CrN.
Another interesting observation is that the ground state
bond length ͑r0͒ of 0.1563 nm for CrN is the shortest among
the 3d nitrides reported to date. This seems to suggest that
the three nonbonding electrons play only minor roles in
weakening the CrwN triple bond. The excited state bond
length ͑r0͒ of 0.1585 nm is very close to that of the ground
state, implying that the excited 4␲ orbital is mainly non-
bonding.
aBands seem to be perturbed.
metal oxides.41 We have added the metal p orbitals since
several ab initio calculations have shown they are somewhat
relevant to the nonbonding ␲ orbitals.
The comparison with the isovalent VO molecule is very
helpful. However, the number of CrN excited states within
the same energy range should be significantly reduced over
that in VO where a small energy gap between the nonbond-
ing 9␴ and 1␦ orbitals results in a particular complicated
electronic structure.41 This difference between the two mol-
ecules can be understood by comparing the atomic spectros-
copy of vanadium and chromium. The gap between the Cr
4s and 3d orbitals must be quite large such that the ground
state of Cr has a d5s1 configuration with the d4s2 configu-
ration much higher in energy.45 Similarly, in CrN, the non-
bonding 9␴ orbital should be significantly higher in energy
than the nonbonding 1␦ orbitals. As a result, the low-lying
states of CrN are derived only from 1␦29␴1, 1␦29␴010␴1, and
1␦29␴04␲1 configurations. A molecular energy level diagram
can then be adapted ͑Fig. 3͒ from that of VO41 by keeping
only these three configurations.
C. Perturbations and other excited states
4
There are two signatures of perturbation in the ⌸ ex-
cited state: ͑i͒ the spacing among different sublevels is not
even and ͑ii͒ several sublevels seem to be perturbed such that
the deviation with a case ͑a͒ effective Hamiltonian fit is no-
ticeable. Since the electronic structure of the CrN A state is
quite similar to that of the B state of VO, the pattern of
perturbing states may also be compared ͑Fig. 3͒. In the case
The ab initio calculation35 has yielded the first excited
state with a 1␦29␴04␲1 configuration which is consistent with
our MO diagram and can be used to assign the 745 nm tran-
sition. The corresponding excited state for VO, however, is
2
of VO, two other states perturb the B state, the ⌸ from
4
the second ⌸ state.41 There are many similarities between
above and 2⌺ϩ on the side. Merer and co-workers have stud-
ied the VO B state extensively and carried out a deperturba-
4
4
the first ⌸ state of CrN and the second ⌸ state of VO.
The observed CrN spin-orbit constant A can be com-
pared with an estimation based on atomic spin-orbit con-
4
2
tion analysis of the interacting B ⌸-a ⌺ϩ states.51 The
4
stants. The ⌸5/2 state can be expressed by a Slater determi-
nant ͉␦ϩ␣␦Ϫ␣␲ϩ␣͘. The molecular spin-orbit constant is
FIG. 3. Energy level diagram of the electronic states of CrN. Solid lines
indicate the observed electronic states whereas the dashed line points to the
2⌺ state inferred from perturbation.
4
FIG. 2. The qualitative CrN molecular orbital diagram and the ⌺Ϫ ground
state electron configuration.
J. Chem. Phys., Vol. 106, No. 11, 15 March 1997
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4388
Balfour, Qian, and Zhou: Electronic spectroscopy of CrN
observed CrN A state energy pattern mirrors that of the de-
perturbed VO B state. The uneven pattern can be associated
with off-diagonal matrix elements with the higher ⌸ state,
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state. Another possible perturber is the ⌬ state from the 1␦3
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matrix employed in the VO analysis in our least squares fit.
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4
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1
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4
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4
4
S.-C. Cheung for helpful comments regarding the ⌸← ⌺Ϫ
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J. Chem. Phys., Vol. 106, No. 11, 15 March 1997
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