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Millimeter-wave spectrum of germanium dichloride GeCl2. Equilibrium structure and anharmonic force field
Journal of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 352/353 (1995)407-415
Millimeter-wave spectrum of germanium dichloride GeC12. Equilibrium structure and anharmonic force field Masaki J. Tsuchiya, Hiroaki Honjou, Keiichi Tanaka*, Takehiko Tanaka Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-81, Japan
Received 18 October 1994
Abstract
The millimeter-wave spectrum of germanium dichloride GeC12 produced in a glow discharge of germanium tetrachloride was observed for several isotopic species in the ground and vibrationally excited states, ul, u2, 2u2, and us. The analysis of the rotational spectra yielded the equilibrium molecular structure, re = 2.169 452(15)/~ and 0e = 99.882 5(15)°, and the harmonic and anharmonic force constants up to the third order.
1. Introduction
In the course of the search for the millimeterwave spectrum of the germanium monochloride radical GeCI" [1] in a glow discharge of germanium tetrachloride GeCI4, we observed a large number of intense spectral lines. These signals seemed, however, to originate from a species with a lifetime somewhat longer than that expected for the GeCI" radical. The most probable candidate for this species was obviously germanium dichloride GeC12. The predicted spectral pattern based on the molecular structure of GeCI2 derived from an electron diffraction study [2] agreed fairly well with the observed pattern. It was finally concluded that germanium dichloride was in fact the carder, because the spectra of the major isotopic species involving germanium isotopes with atomic mass ¢~Dedicatedto ProfessorYonezo Morino on his 87th birthday. * Corresponding author. Email: [email protected]; fax: (+ 81)92-632-2734.
numbers of 70 (20.5%), 72 (27.4%), 74 (36.5%), and 76 (7.8%), and chlorine isotopes with mass numbers of 35 (75.8%) and 37 (24.2%), were subsequently identified, where the figures in parentheses are the natural abundances of the isotopes. In this paper we report the millimeter-wave spectrum of germanium dichloride in the ground and vibrationally excited states, v l, v2, 2v2, and v3, including various isotopic species. The equilibrium molecular structure and the third-order anharmonic force constants were deri,~ed from the rotational constants and compared With those of related molecules. Infrared spectra of germanium dichloride have been studied in a low-temperature Ar m~trix [3,4], and Raman spectra have been recorded in the gas phase [5] and in an N2 matrix [6] to give the fundamental vibrational frequencies: vl Cs-stretch) ~ 3 9 9 cm -l, v2 (bend) ~ 1 5 9 cm -1 [5], and v 3 (a-stretch) ~ 372 cm -z [4]. The molecular structure was investigated by electron diffraction [2], and recently by ab initio calculations [729]. The
0022-2860/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0022-2860(95)08830-X
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M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
electric dipole moment was calculated to be 2.956 D [8]. Microwave spectra of the XY2-type triatomic molecules composed of atoms in groups 14 and 17 have been studied for CF2 [10], CC12 [11], SiF2 [12-14], SiCI2 [15,16], and GeF2 [17,18]. In most cases, the equilibrium structure was determined accurately from the rotational spectra in vibrationally excited states.
2. Experimental A newly revised 83 kHz source modulation spectrometer equipped with a free-space absorption cell at Kyushu University has been used for the present measurements. Millimeter-wave radiation of 100172 GHz was generated by a Millitech frequency doubler (MU2-06-T) driven by Oki klystrons in the frequency range of 50-86 GHz, and detected by a photoconductive InSb detector (Infrared Laboratory) cooled down to liquid-He temperature. The source frequency was modulated to a full width of about 300 kHz and simultaneously scanned in the range 5-10 MHz with a repetition rate of 5 Hz, by a bipolar square wave and a triangular wave, respectively, superimposed on the reflector voltage of the klystron. The beat between the millimeterwave frequency and a stable X-band freuqency locked to a frequency synthesizer was measured by an all-wave receiver tuned to a few megahertz. The output of the InSb detector was demodulated in 2f mode by a phase-sensitive detector (PSD) operating at 83 kHz to give a second derivativelike line shape. The PSD output with a time constant of 1 ms was accumulated in a microcomputer for several hundred scans. The microcomputer also controlled the frequency of the synthesizer. The overall accuracy of the observed frequency was estimated to be better than 30 kHz. Details of our spectrometer have been described in our previous papers [19,20]. In an early stage of the present research, germanium dichloride was produced by a dc glow discharge in germanium tetrachloride. A free space-type absorption cell consisted of a Pyrex tube of 1.3 m length and 10 cm outer diameter. This was sealed by Teflon convex lenses with a
focal length of 35 cm and contained two 5 cm long cylindrical stainless steel electrodes separated by about 1 m. Pure germanium tetrachloride was flowed through the absorption cell at a pressure of about 25 mTorr and pumped out by a booster pump backed up by a rotary pump. The optimum discharge current for the production of GeC12 was about 30 mA. At a later stage, we used the reaction of gaseous germanium tetrachloride with heated germanium metal [2] to produce GeC12 more effectively than by the discharge method. A quartz tube of 15 mm inner diameter, located at the inlet to the absorption cell, was filled with grains of metallic germanium and heated to about 500°C by an electric furnace. Pure germanium tetrachloride at a pressure of 15 mTorr was flowed through the quartz tube. The reaction product was entered directly into the cell and pumped out by a combination of a booster pump and a rotary pump. Spectra in the ground and u2 fundamental states were mostly observed by the discharge method. However, the thermal reaction without discharge was utilized for the recording of spectra for the higher vibrationally excited states, u~, u3, and 2u2, and for less abundant isotopic species.
3. Observed spectrum and analysis During the spectral search for the GeCI" radical in the discharge plasma of GeCI4, a cluster of strong signals was accidentally observed in the 144 GHz range. These signals originated from neither the GeCI" radical nor the GeC1÷ ion. The carrier of the spectrum seemed to be more stable than such transient species, as the spectrum was even observed in the dc discharge under sealed-off conditions. We considered GeC12 and GeC13 to be among the plausible candidates, and also GeHCI3, GeH2CI2, and GeH3C1, as hydrogen is easily supplied from water adsorbed on the surface of the sample cell. However, the observed spectrum was consistent neither with the reported lines of GeHC13 [21], nor with those of GeH3CI [22]. Similar clusters of strong signals were then observed in the frequency ranges near 147 and 151 GHz, which are shifted to high frequency by
M.J. Tsuchiya et al./Journal o f Molecular Structure 352/353 (1995) 407-415
3.8 and 7.6 GHz, respectively, from where the first spectrum was observed. The predicted spectral pattern based on the molecular structure of GeC12 from the electron diffraction study [2] accounted for the observation fairly well; R-branch transitions obeying b-type selection rules give rise to clusters repeated every 3.80 GHz, which corresponds to twice the C rotational constant. Three more series of clusters with similar patterns were soon identified, which were displaced from the first series by less than 1 GHz towards the high frequency. Three out of the four series found were assigned as originating from the abundant isotopic species, 74Ge35C12 (21.0%), 72Ge35C12 (15.7%), and 7°Ge35C12 (11.8%), of germanium dichloride in the ground state, on the basis of the isotopic relation between the rotational constants. The remaining series, which did not fit with the isotopic relation, was assigned to the spectrum in the u2 vibrational state of the most abundant species 74Ge35C12. Fig. 1 illustrates typical lines of 74Ge35C12 in the ground and u2 states, with K-type doubling caused by asymmetry. The component of the doublet corresponding to o d d values of K, + K~ (denoted as (co) in Fig. 1) is stronger than that with even values of Ka + Kc (00). The observed intensity ratio is consistent with the ratio 10:6 predicted
eo
oo
124578
X 3 I
124200
1242114
124408
124412 M H z
Fig. 2. Rotational transitions with resolved K-type doubling, 302,28 ~--293.27 and 303,28 ~--292,27 , of 74Ge35C12 in the ua (right) and u 3 (left) states. The intensity ratio of the K-doublet components for the Ul state is the same as those for the ground and u 2 states in Fig. 1, whereas for the u 3 state the ratio is reversed, i.e. (co): (oo) - 6: 10.
from the spin statistics of the chlorine, nucleus (I = 3/2), assuming Czv symmetry and an 1Al ground electronic state. Measurements of the weaker signals were carried out using the thermal reaction rather khan the discharge method. We finally observed more than one thousand signals originating from GeC12 in the frequency range 108-160 GHz. Some of them were assigned to the spectra of the higher vibrationally
Isotope
State
nrot
Jmaxa
Kmaxa
a (kHz) b
74Ge35C12
Ground ul v,2 u3 2u 2
84 30 86 28 61
38 32 41 32 39
6 4 5 4 5
23 16 25 14 22
72Ge35C12
Ground u2 2u2
48 60 24
38 41 32
6 5 5
t5 16 15
V°Ge3SCl2
Ground
44
38
6
12
76Ge35C12
Ground
29
32
5
12
I
124386
I111
e()
/o
124382
V~
e()
O0
eO
I
V3
Table 1 Profile of the data included in the least-squares analysis
(;rnund
V2
409
124582 M H z
Fig. 1. Rotational transitions with resolved K-type doubling. 302,28 -*--293.27 and 303,28 +-- 292,27, of 74Ge35C12 in the ground (right) and u2 (left) states. One c o m p o n e n t (denoted as co) of the K-type doublet is stronger than the other (oo) (see text), obeying the spin statistics for the chlorine nucleus. The observed line intensities are consistent with the calculated ratio of 10 : 6.
a M a x i m u m values of the rotational q u a n t u m numbers J and
Ko. b Standard deviation in the least-squares analysis.
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
410
Table 2 Observed microwave spectrum of 74Ge35C12 in the ground state Observed (MHz)
Rotational transition
O - Ca (kHz)
J'
K~,,
K~,,
J"
K~
K~'
28 28 27 27 26 26 25
0 1 2 1 2 3 3
28 28 26 26 24 24 22
27 27 26 26 25 25 24
1 0 1 2 3 2 4
27 27 25 25 23 23 21
109195.674 109195.674 109221.828 109221.828 109276.028 109295.415 109173.096
-14 -17 -260 b 55 b -58 -23 -122 b
29 29 28 28 27 27 26 25
0 1 2 1 2 3 3 5
29 29 27 27 25 25 23 21
28 28 27 27 26 26 25 24
1 0 1 2 3 2 4 4
28 28 26 26 24 24 22 20
113024.513 113024.513 113049.816 113049.816 113103.194 113113.797 113095.707 116791.104
-1 -2 -54 c 1094 -24 -39 -28 18
30 30 29 29 28 28 27
0 1 2 1 2 3 3
30 30 28 28 26 26 24
29 29 28 28 27 27 26
1 0 1 2 3 2 4
29 29 27 27 25 25 23
116853.138 116853.138 116877.621 116877.621 116928.996 116934.833 116974.286
17 17 394 124c -26 23 71
31 31 30 30 29 29 27
0 1 2 1 2 3 4
31 31 29 29 27 27 23
30 30 29 29 28 28 26
1 0 1 2 3 2 5
30 30 28 28 26 26 22
120681.517 120681.517 120705.150 120705.150 120754.214 120757.378 120019.849
17 17 -30 ¢ 144 19 46 3
32 32 31 31 30 30 28
0 1 2 1 2 3 4
32 32 30 30 28 28 24
31 31 30 30 29 29 27
1 0 1 2 3 2 5
31 31 29 29 27 27 23
124509.656 124509.656 124532.618 124532.618 124579.118 124580.796 124247.964
14 14 -13 10 24 12 52
34 34 33 33 32 32 31 31 30
0 1 2 1 2 3 4 3 5
34 34 32 32 30 30 28 28 26
33 33 32 32 31 31 30 30 29
1 0 1 2 3 2 3 4 4
33 33 31 31 29 29 27 27 25
132165.155 132165.155 132186.985 132186.985 132229.045 132229.045 132337.341 132315.491 132857.934
-30 -30 -14 -8 406 b -78 b -35 -99 b -140 b
Table 2 Continued Observed (MHz)
Rotational transition
O-C a (kHz)
J'
K~,~
K~¢.
J"
K'~
K~'
30 29
4 6
26 24
29 28
5 5
25 23
132287.079 137353.495
82 b 23
35 35 34 34 33 33 32 32 31 31 30 30
0 1 2 1 2 3 4 3 5 4 6 5
35 35 33 33 31 31 29 29 27 27 25 25
34 34 33 33 32 32 31 31 30 30 29 29
1 0 1 2 3 2 3 4 4 5 5 6
34 34 32 32 30 30 28 28 26 26 24 24
135992.546 135992.546 136013.849 136013.849 136053.444 136053.444 136149.290 136137.108 136531.770 136191.121 136668.526 134234.430
-22 -22 -28 -25 79 b -179 b 13 9 -33 120 b -61 32
36 36 35 35 34 34 33 33 32 32 31 31
0 1 2 1 2 3 4 3 5 4 6 5
36 36 34 34 32 32 30 30 28 28 26 26
35 35 34 34 33 33 32 32 31 31 30 30
1 0 1 2 3 2 3 4 4 5 5 6
35 35 33 33 31 31 29 29 27 27 25 25
139819.673 139819.673 139840.549 139840.549 139878.124 139878.124 139964.298 139957.526 140256.725 140055.542 142424.179 138908.784
-8 -8 18 20 704 -66 c -27 -35 -38 -13 6 -30
37 37 36 36 35 35 34 34 33 33 32 32
0 1 2 1 2 3 4 3 5 4 6 5
37 37 35 35 33 33 31 31 29 29 27 27
36 36 35 35 34 34 33 33 32 32 31 31
1 0 1 2 3 2 3 4 4 5 5 6
36 36 34 34 32 32 30 30 28 28 26 26
143646.533 143646.533 143666.997 143666.997 143702.663 143702.663 143781.409 143777.598 144014.261 143896.617 145512.955 143281.639
16 16 52 53 -17 c -884 24 -52 -53 -41 24 -33
38 38 37 37 36 36 35 35
0 1 2 1 2 3 4 3
38 38 36 36 34 34 32 32
37 37 36 36 35 35 34 34
1 0 1 2 3 2 3 4
37 37 35 35 33 33 31 31
147473.032 147473.032 147493.149 147493.149 147527.238 147527.238 147599.748 147597.713
-35 -35 42 42 244 -14 c -5 12
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415 Table 2 Continued Rotational transition
Observed (MHz)
s'
/~'o
~'c
s"
/C
/<'
34 34 33 33
5 4 6 5
30 30 28 28
33 33 32 32
4 5 5 6
29 29 27 27
0 - Ca (kHz)
411
frequencies, which are not presented in this paper, are available on request from the authors or the editorial office of the journal.l 4. Results and discussion
147792.477 147724.368 148840.413 147446.880
-14 82 68 25
a Observed frequency minus calculated frequency in kHz. b Blended lines, not used in the analysis. c Unresolved K-doublet, weighted with 0.625. d Unresolved K-doublet, weighted with 0.375.
excited states, vl, v3, and 2v2, as well as those of the minor isotopic species as 76Ge3SC12 (4.5%). Fig. 2 shows the signals assigned to the vl and v 3 states. In the case of the K-doublet component, the signals for the Vl state have the same intensity ratio as for the ground and v2 states. In contrast, the signals of the v3 state have the reverse ratio 6 : 10 for odd and even values of K~ + K,., because the v3 vibration is due to antisymmetric stretching and belongs to the b 2 symmetry species of the C2~ point group. The intensity ratio of the K-doublet components gave us the definitive assignment of the vibrational state. The intensities of the Vl and v 3 state lines were 2 0 - 3 0 % of those of the ground state lines, consistent with the vibrational frequencies. No hyperfine splittings due to the chlorine nuclear quadrupole were resolved for the lines observed in the present work. The transition frequencies measured in the present study were subjected to a least-squares fit, in which the effective Hamiltonian in Watson's A-reduced form [23], including the quartic centrifugal distortion constants, was used. Table 1 summarizes the profile of the data included in the analysis, where nrot is the number of observed rotational transitions, and Jmax and Kmax are the largest J and/Ca values covered, respectively. The spectra of minor isotopic species, involving 73Ge and 37C1, were excluded from the analysis, because of weak intensities and for the sake of simplicity. The observed frequencies of the main species 74Ge35C12 in the ground vibrational state are listed in Table 2 with their assignments and the o b s e r v e d - calculated ( O - C) values. Tables of
4.1. Equilibrium molecular structure The molecular constants of various isotopic species obtained by least-squares analysis are summarized in Table 3. For the 74Ge3SClz and 72Ge35C12 species, the molecular constants of the four (v l, V2, 2u2, and v3) and two (V2 and 2u2) vibrationally excited states, respectively, were derived, as well as those of the ground state. The uncertainties in parentheses correspond to one standard deviation of the fit. In some cases, the centrifugal distortion constants /Sj and 6K were fixed to the values in the ground or v2 s~ate. The inertia defects calculated from the observed rotational constants are also given in Table 3. The rotational constants of the V4Ge35C12 and 72Ge35C12 species were fitted to the formula B,, = Be - .iB(vl q- 1/2) - c~g(v2 + 1/2) - o~B(v3 q- 1/2) + "yB2(l,2 --~ 1/2) 2
(1)
The vibration-rotation constants % (v = 1, 2, and 3) and "Y22are given in Table 4 with their uncertainties corresponding to one standard devialtion. The c~2 and 722 values behave as expected for the two isotopic species. The equilibrium rotational constants derived by Eq. (1) are summarized in Table 5 together with the inertia defect calculated from these constants. As discussed in our previous paper [24] and the references cited therein [25-28], the rotational constants derived from the A-reduced form Hamil~onian are slightly different from the values corresponding to the real equilibrium structure. We made corrections corresponding to causes (2) and (3) in Ref. [24], using the centrifugal distortion constants calculated from the harmonic force field in Table 8. However, cause (4), the effect of electron orbital motion coupled with molecular rotation, was
i Data deposited with BLLD as Supplementary Publication number SUP26522 (21 pages).
412
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
Table 3 Molecular constants and inertia defect of germanium dichloridea Constant
A B C As Aj~ AK 6j t5K
74Ge35C12
Unit
Ground
vl
v2
v3
2v2
7229.653(13) 2613.0356(24) 1916.07269(42)
7231.873(83) 2604.1902(32) 1913.9420(11)
7291.478(42) 2609.0548(57) 1911.75535(43)
7197.727(63) 2610.2424(44) 1909.7690(12)
7354.093(26) 2605.1122(24) 1907.43491(45)
1.21882(64) -7.367(26) 38.46(47) 0.45234(fix) 1.834(fix)
1.19796(17) --8.096(10) 44.66(18) 0.4407(fix) 1.916(fix)
kHz kHz kHz kHz kHz
2.23628(65)
u A2
1.2254(12) --7.674(45) 37.89(46) 0.45234(63) 1.834(31)
A
1.22960(59) -7.890(34) 39.44(46) 0.45234(fix) 1.834(fix)
0.44725(59)
Constant
A B C Aj ASK AK ~g 6K A
1.1999(66) --7.62(10) 41.7(17) 0.4407(33) 1.916(96)
0.10542(111)
1.34053(90)
72Ge35C12
0.80083(102) 7°Ge35C12
76Ge35C12
MHz MHz MHz
Unit
Ground
/-'2
2u2
Ground
Ground
7327.383(25) 2612.9953(39) 1922.87028(79)
7390.037(28) 2609.0402(19) 1918.52667(30)
7453.067(69) 2605.1186(34) 1914.1785(10)
7430.472(22) 2612.9749(37) 1929.90755(67)
7137.378(35) 2613.0636(47) 1909.4958(10)
1.2207(21) --7.834(36) 40.35(57) 0.4468(11) 1.801(32)
1.20587(11) --7.8829(73) 44.18 (18) 0.4407(fix) 1.916(fiX)
1.20199(54) --8.568(27) 49.61 (71 ) 0.4407(fix) 1.916(fiX)
1.2254(19) --8.148(29) 41.81 (49) 0.44588(99) 1.760(26)
1.21514(52) --7.324(21) 38.20(35) 0.45234(fix) 1.834(fiX)
kHz kHz kHz kHz kH z
1.33081(62)
2.21593(97)
0.44121(71)
0.45404(86)
u A2
0.44420(74)
MHz MHz MHz
a la uncertainties in the unit of the last digit are in parentheses.
d i s r e g a r d e d , since the r o t a t i o n a l g values o f G e C I 2 have n o t been r e p o r t e d . T h e c o r r e c t e d e q u i l i b r i u m r o t a t i o n a l c o n s t a n t s a n d inertia defect Table 4 Vibration-rotation constants of germanium dichloride in MHza 74Ge35C12 ~1
72Ge35C12 v2
~3
//2
a n -2.220(84) -61.035(131) 31.926(64) -62.278(120) c~B 8.8454(40) 4.0190(179) 2.7932(50) 3.9886(102) c~c 2.1307(12) 4.3142(16) 6.3037(13) 4.3391(21) 7n 7B 3'c
-
0.395(44)
-
0.0191(59)
-
0.188(46)
0.0168(32)
-0.00155(53)
-
-0.00228(70)
a hr uncertainties in the unit of the last digit are in parentheses.
are c o m p a r e d in T a b l e 5 with the u n c o r r e c t e d values. In b o t h cases, the inertia defect has a small negative value, as is often the case for a p l a n a r t r i a t o m i c molecule. The c o r r e c t e d value Ae = - 0 . 0 0 4 7 5 ( 1 4 4 ) u A 2 is slightly larger in the a b s o l u t e value t h a n the u n c o r r e c t e d one, the difference c o r r e s p o n d i n g to the effect o f centrifugal d i s t o r t i o n . The residual inertia defect m a y be a t t r i b u t e d to the electronic t e r m Aelec due to the r o t a t i o n a l g values, a n d the higher o r d e r v i b r a t i o n - r o t a t i o n c o n s t a n t s neglected in this analysis. T h e b o n d length r e a n d b o n d angle 0e were calc u l a t e d f r o m the c o r r e c t e d e q u i l i b r i u m m o m e n t s o f inertia. T h r e e different sets o f values are derived f r o m the c o m b i n a t i o n s o f the m o m e n t s , which slightly differ f r o m each o t h e r because o f the
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415 Table 5 Equilibrium structure of germanium dichloride a Equilibrium rotational constants b Ae 7213.890 4- 0.083 MHz Be 2620.8596 ± 0.0103 MHz Ce 1192.4474 + 0.0016 MHz Inertia defect 2x~ -0.00272 4- 0.00143 u / k 2 Corrected equilibrium rotational constants c A~ 7213.879 ± 0.083 MHz Be 2620.8515 4- 0.0103 MHz Ce 1922.4570 ± 0.0017 MHz Inertia defect A~ -0.00475 ± 0.00144 u/~2 Bond length d (1~, Ib) 2.1694670 + 0.0000052 ,~ (In, Ic) 2.1694513 ± 0.0000033/~ (Ib, I,.) 2.1694365 4- 0.0000040 ,~ Average 2.1694516/~ Bond angle d
(la, lb) (I~, Ic) (lb, 4) Average
99.88212 99.88142 99.88403 99.88252
+ 0.00050 ° ± 0.00051 ° + 0.00060 ° °
a Errors correspond to 1a. Derived from the data of 74Ge35C12. b Derived from the constants in the Watson's A-reduced form Hamiltonian. c Corrected for the centrifugal distortion constants (see text). d Derived from the corrected equilibrium constants.
finite equilibrium inertia defect. The average values of the three sets are
413
and the harmonic force field in Table 8 as r z = 2 . 1 7 3 0 1 4 ( 6 ) /k and 0 z = 9 9 . 9 8 6 3 ( 6 ) °. The structural parameters given by the electron diffraction study [2] are r a = 2 . 1 8 3 ( 4 ) /~ and 0a = 100.3(4) °. The ra value is considerably larger than rz and r e. The r0 structure of CC12 is r 0 - 1 . 7 1 5 7 ( 2 8 ) /k and 00 = 109.2(3) ° [11], and the equilibrium structure of SiC12 is r e = 2 . 0 6 5 3 1 0 ( 2 6 ) • and 0e = 101.3240(16) ° [16]. The bond length of GeC12 is longer than those of CC12 and SiCI2 by 0.4537 A and 0.1041 A, respectively. For these homologous molecules, the bond length increases almost linearly with covalent bond radius, The bond angle of GeCI 2 is smaller than those of CC12 and SIC12 by 9.3 and 1.44 °, respectively. 4.2. Intramolecular f o r c e field
The inertia defect of 74Ge35C12 in the ground state and its vibrational changes are summarized in Table 6. The squared Coriolis coupling constants (~13)2 listed in Table 6 were calculated from the vibrational changes, where we used the u 1 and u2 vibrational frequencies from Raman spectroscopy [5] and the u 3 value from IR spectroscopy [4]. The (¢J3) c 2 values derived from the inertia defects in the u I and u 3 states are about 9% larger than the values from u2 and 2u2, the differences probably being ascribable to uncertainties in the Table 6 Inertia defects and squared Coriolis coupling constants a
r e = 2.169452 4-0.000015/~ 0e = 99.882 5 4- 0.001 5 ° where the uncertainties are estimated from the discrepancies. The molecular structures determined by the recent ab initio calculations, re = 2.177 A and 0e -- 100.35 ° [7], r e = 2.191 /k and 0e = 100.5 ° at the M R S D C I level [8], and r e = 2.182 /k and 0e = 99.95 ° at the MP2 L A N D L 1 D Z * level [9], agree well with the present equilibrium values; the discrepancies are at most 1.0 and 0.6%, respectively, for the bond length and bond angle. The r z structure w a s calculated from the rotational constants in the ground state of 74Ge35C12
Inertia defect Ground 0.44725 5:0.00059 u A 2 Change from the ground state value uI -0.34183 -t- 0.00126 u •2 u2 0.89328 ± 0.00108 u/]2 u3 0.35358 + 0.00118 u A 2 2u 2 1.78903 + 0.00088 u A 2 Squared Coriolis coupling constants (~3) 2 uI 0.15213 4- 0.00056 u2 0.13923 4- 0.00104 u3 0.15231 ± 0.00051 2u 2 0.13804 5:0.00043 Average 0.14568 b a Errors correspond to 1cr. Derived from the data of 74Ge35C12. b Averaged value of the vl and v2 states.
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
414
Table 7 Centrifugal distortion constants of 74Ge35C12 in kHz Constants As
Asx AK ~j t~K
7"aaaa ~-bbbb ~-~ ~'1 72 ATe
Observed a 1.2482(90) -7.945(181) 34.61(252) 0.4625(47) 1.762(155) --111.65(1011) --8.6928(521) --1.2928(521) 16.802(732) 1.676(149)
Calculated b 1.290 -7.535 36.37 0.469 1.947 --120.5 --8.913 -1.409 14.66 1.24
observed values. The Coriolis coupling constants ((~3) 2 calculated for the 74Ge35C12 and 72Ge35C12 species are 0.146 and 0.151, respectively. The av constants of the 74Ge35C12 species listed in Table 4 were subjected to the analysis to determine the third-order anharmonic force constants, following the procedure described by Kuchitsu and Morino [30]. The definition of the anharmonic force constants is Vanh = (1/6)frrr(Ar ~ q-
+ (1/2)frr~'(Arl + Ar2)ArlAr2 + (1/2)frro(Ar 2 +
-0.012(215)
The equilibrium values, la uncertainties are in parentheses. b Calculated from the harmonic force constants in Table 8. c KirchhotVs ~- planarity defect.
Ar~) Ar~)AO +fr/oArl Ar2AO
+ (1/2)froo(Arl + Ar2)AO 2 + ( 1 / 6 ) J ~ 0 0 A 0 3
(2)
a
reported vibrational frequencies. If we assume the energy difference between ul and u3 to be smaller than the literature value [4,5] by 2 cm -l, the ((~3) 2 values derived from the u 1 and u3 states agree with those from the u2 and 2u2 states. The ((~3) 2 values for the 72Ge35C12 species, 0.145 7(9) and 0.146 4(6), derived from the inertia defects in the u 2 and 2u 2 states, respectively, are similar to the corresponding values for the normal species. Equilibrium centrifugal distortion constants in the A-reduced form are calculated by applying Eq. (1) and the results are summarized in Table 7 for the 74Ge35C12 species. The "rxxxx (x = a,b, c) constants are calculated from the equilibrium values of A j, A j/c, A/(, and 6j, and the -q term from A s and As/( , as shown in Table 7. The planarity defect by Kirchhoff [29], A T = -0.012(215) kHz, is essentially zero, as expected for the equilibrium constants of a planar molecule. The squared Coriolis coupling constant was combined with the fundamental vibrational frequencies to determine the harmonic force field. The resulting harmonic force constants are listed in Table 8. The uncertainties in the harmonic force constants reflect the uncertainties in the squared Coriolis coupling constant ( ~ 5%) and the vibrational frequencies ( ~ 1%). The centrifugal distortion constants calculated from the harmonic force constants are compared in Table 7 with the
The harmonic force field was fixed as above. The determined constants are given in Table 8 with errors estimated from uncertainties in the av constants. Table 8 also lists the cubic potential constants kill, etc., for the 74Ge35C12 species. The oQ constants calculated for the 72Ge35C12 species, Table 8 Force constants of germanium dichloride GeCI2
SiCI2a
GeF2 b
Unit
1.7321 A 97.17 deg
re 0e
2.16945(2) 99.8825(15)
2.06531(3) 101.3240(16)
fr f~e frO
2.066(34) 0.232(34) --0.010(55) 0.90(17)
2.535(23) 0.278(23) 0.120(2) 1.053(2)
4.08 0.26 --0.01 0.96
mdyn A -1 mdyn A -j mdyn mdyn A
-8.95(35) -0.102(35) 0.078(96) -0.266(53) -0.685(90) -2.321(95)
-11.75(15) -0.208(20) -0.389(17) -0.464(13) -1.129(23) -2.826(14)
-22.65 -0.26 -0.07 -0.36 -0.81 -2.23
mdyn A -2 mdyn A 2 mdyn A -1 mdyn A l mdyn mdyn A
-13.499(76) -11.876(26) 3.04(11) -4.599(8) -58.80(49) 0.157(23)
-23.90 -9.23 8.42 -7.37 -77.53 1.06
cm -1
)Co f~rr frr/ frro f~e0 fro0
fooo
kill c -10.27(12) ktl 2 k122
-5.67(12) 3.496(14) kz22 -3.8613(15) kl33 -37.49(40) k233 0.65(14)
a Ref. [16]. b Ref. [17]. c For main isotopic species.
c m -1 ~3.1-1
cm
1
cm- 1 cm- 1
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
a A = - 6 1 . 8 MHz, a~ = 4.0 MHz, and a c = 4.3 MHz, reproduce well the observed values listed in Table 4. In Table 8, the harmonic and anharmonic force constants of GeCI2 were compared with those of SiCI 2 [16] and GeF2 [17]. The stretching force constants fr and frrr of GeC12 are much weaker (by about 20% and 50-60%, respectively) than those of SiC12 and G e F 2, corresponding to the longer bond length (by about 5 and 25%). The fro constant of SiCI 2 is positive, whereas those for GeCI2 and GeF2 are essentially zero. The bending force constants fo and fooo are smaller (by about 15%) than those of SiCI 2, but almost equal to those of GeF2.
Acknowledgments We thank the Kurata Science Foundation, Itoh Science Foundation, and Iketani Science Foundation, for financial support. Calculations for the present study were carried out at the Computer Center of Kyushu University.
References [1] K. Tanaka, M.J. Tsuchiya and H. Honjou, in preparation. [2] Gy. Schultz, J. Tremmel and I. Hargittai, J. Mol. Struct., 55 (1979) 207. [3] L. Andrews and D.L. Frederick, J. Am. Chem. Soc., 92 (1970) 775. [4] J.H. Miller and L. Andrews, J. Mol. Struct., 77 (1981) 65. [5] I.R. Beattie and R.O. Perry, J. Chem. Soc. (A), (1970) 2429. [6] G.A. Ozin and A.V. Voet, J. Chem. Phys., 56 (1972) 4768.
415
[7] J.M. Coffin, T.P. Hamilton, P. Pulay and I. Hargittai, Inorg. Chem., 28 (1989) 4092. [8] M. Benavides-Garcia and K. Balasubramanian, J. Chem. Phys., 97 (1992) 7537. [9] J. Karolczak, Q. Zhuo, D.J. Clouthier, W.M. Davis and J.D. Goddard, J. Chem. Phys., 98 (1993) 60. [10] A. Charo and F.C. DeLucia, J. Mol. Spectrosc., 94 (1982) 363. [11] M. Fujitake and E. Hirota, J. Chem. Phys., 91 (1989) 3426. [12] H. Shoji, T. Tanaka and E. Hirota, J. Mol. Spectrosc., 47 (1973) 268. [13] V.M. Rao, R.F. Curl, Jr., P.L. Timms and J.L. Margrave, J. Chem. Phys., 43 (1965) 2557. [14] V.M. Rao and R.F. Curl, Jr., J. Chem. Phys , 45 (1966) 2032. [15] M. Tanimoto, H. Takeo, C. Matsumura, M. Fujitake and E. Hirota, J. Chem. Phys., 91 (1989) 2106. [16] M. Fujitake and E. Hirota, Spectrochim. Acta., Part A, 59 (1994) 1345. [17] H. Takeo, R.F. Curl, Jr. and P.W. Wilson, J. Mol. Spectrosc., 38 (1971) 464. [18] H. Takeo and R.F. Curl, Jr., J. Mol. Spectrosc., 43 (1972) 21. [19] K. Tanaka, T. Okabayashi and T. Tanaka, J. Mol. Spectrosc., 132 (1988) 476. [20] T. Tanaka, K. Kato, T. Okabayashi and K. Tanaka, Rev. Sci, Instrum., 60 (1988) 106. [21] P. Venkateswarlu, R.C. Mockler and W. Gordy, J. Chem. Phys., 21 (1953) 1713. [22] J. Demaison, G. Woldarczak and J. Burie, J. Mol. Spectrosc., 140 (1990) 322. [23] J.K.G. Watson, J. Chem. Phys., 46 (1967) 1935. [24] K. Miyazaki, M. Tanoura, K. Tanaka and T. Tanaka, J. Mol. Spectrosc., 116 (1986) 435. [25] J.K.G. Watson, Mol. Phys., 15 (1968) 479. [26] E.B. Wilson, Jr. and J.B. Haword, J. Chem. Phys., 4 (1936) 260. [27] D. Kivelson and E.B. Wilson, Jr., J. Chem. Phys., 20 (1952) 1575. [28] T. Oka and Y. Morino, J. Mol. Spectrosc., 6 (1961) 472. [29] W.H. Kirchhoff, J. Mol. Spectrosc., 41 (1972) 333. [30] K. Kuchitsu and Y. Morino, Bull. Chem. Soc. Jpn., 38 (1965) 814.
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 352/353 (1995)407-415
Millimeter-wave spectrum of germanium dichloride GeC12. Equilibrium structure and anharmonic force field Masaki J. Tsuchiya, Hiroaki Honjou, Keiichi Tanaka*, Takehiko Tanaka Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-81, Japan
Received 18 October 1994
Abstract
The millimeter-wave spectrum of germanium dichloride GeC12 produced in a glow discharge of germanium tetrachloride was observed for several isotopic species in the ground and vibrationally excited states, ul, u2, 2u2, and us. The analysis of the rotational spectra yielded the equilibrium molecular structure, re = 2.169 452(15)/~ and 0e = 99.882 5(15)°, and the harmonic and anharmonic force constants up to the third order.
1. Introduction
In the course of the search for the millimeterwave spectrum of the germanium monochloride radical GeCI" [1] in a glow discharge of germanium tetrachloride GeCI4, we observed a large number of intense spectral lines. These signals seemed, however, to originate from a species with a lifetime somewhat longer than that expected for the GeCI" radical. The most probable candidate for this species was obviously germanium dichloride GeC12. The predicted spectral pattern based on the molecular structure of GeCI2 derived from an electron diffraction study [2] agreed fairly well with the observed pattern. It was finally concluded that germanium dichloride was in fact the carder, because the spectra of the major isotopic species involving germanium isotopes with atomic mass ¢~Dedicatedto ProfessorYonezo Morino on his 87th birthday. * Corresponding author. Email: [email protected]; fax: (+ 81)92-632-2734.
numbers of 70 (20.5%), 72 (27.4%), 74 (36.5%), and 76 (7.8%), and chlorine isotopes with mass numbers of 35 (75.8%) and 37 (24.2%), were subsequently identified, where the figures in parentheses are the natural abundances of the isotopes. In this paper we report the millimeter-wave spectrum of germanium dichloride in the ground and vibrationally excited states, v l, v2, 2v2, and v3, including various isotopic species. The equilibrium molecular structure and the third-order anharmonic force constants were deri,~ed from the rotational constants and compared With those of related molecules. Infrared spectra of germanium dichloride have been studied in a low-temperature Ar m~trix [3,4], and Raman spectra have been recorded in the gas phase [5] and in an N2 matrix [6] to give the fundamental vibrational frequencies: vl Cs-stretch) ~ 3 9 9 cm -l, v2 (bend) ~ 1 5 9 cm -1 [5], and v 3 (a-stretch) ~ 372 cm -z [4]. The molecular structure was investigated by electron diffraction [2], and recently by ab initio calculations [729]. The
0022-2860/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0022-2860(95)08830-X
408
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
electric dipole moment was calculated to be 2.956 D [8]. Microwave spectra of the XY2-type triatomic molecules composed of atoms in groups 14 and 17 have been studied for CF2 [10], CC12 [11], SiF2 [12-14], SiCI2 [15,16], and GeF2 [17,18]. In most cases, the equilibrium structure was determined accurately from the rotational spectra in vibrationally excited states.
2. Experimental A newly revised 83 kHz source modulation spectrometer equipped with a free-space absorption cell at Kyushu University has been used for the present measurements. Millimeter-wave radiation of 100172 GHz was generated by a Millitech frequency doubler (MU2-06-T) driven by Oki klystrons in the frequency range of 50-86 GHz, and detected by a photoconductive InSb detector (Infrared Laboratory) cooled down to liquid-He temperature. The source frequency was modulated to a full width of about 300 kHz and simultaneously scanned in the range 5-10 MHz with a repetition rate of 5 Hz, by a bipolar square wave and a triangular wave, respectively, superimposed on the reflector voltage of the klystron. The beat between the millimeterwave frequency and a stable X-band freuqency locked to a frequency synthesizer was measured by an all-wave receiver tuned to a few megahertz. The output of the InSb detector was demodulated in 2f mode by a phase-sensitive detector (PSD) operating at 83 kHz to give a second derivativelike line shape. The PSD output with a time constant of 1 ms was accumulated in a microcomputer for several hundred scans. The microcomputer also controlled the frequency of the synthesizer. The overall accuracy of the observed frequency was estimated to be better than 30 kHz. Details of our spectrometer have been described in our previous papers [19,20]. In an early stage of the present research, germanium dichloride was produced by a dc glow discharge in germanium tetrachloride. A free space-type absorption cell consisted of a Pyrex tube of 1.3 m length and 10 cm outer diameter. This was sealed by Teflon convex lenses with a
focal length of 35 cm and contained two 5 cm long cylindrical stainless steel electrodes separated by about 1 m. Pure germanium tetrachloride was flowed through the absorption cell at a pressure of about 25 mTorr and pumped out by a booster pump backed up by a rotary pump. The optimum discharge current for the production of GeC12 was about 30 mA. At a later stage, we used the reaction of gaseous germanium tetrachloride with heated germanium metal [2] to produce GeC12 more effectively than by the discharge method. A quartz tube of 15 mm inner diameter, located at the inlet to the absorption cell, was filled with grains of metallic germanium and heated to about 500°C by an electric furnace. Pure germanium tetrachloride at a pressure of 15 mTorr was flowed through the quartz tube. The reaction product was entered directly into the cell and pumped out by a combination of a booster pump and a rotary pump. Spectra in the ground and u2 fundamental states were mostly observed by the discharge method. However, the thermal reaction without discharge was utilized for the recording of spectra for the higher vibrationally excited states, u~, u3, and 2u2, and for less abundant isotopic species.
3. Observed spectrum and analysis During the spectral search for the GeCI" radical in the discharge plasma of GeCI4, a cluster of strong signals was accidentally observed in the 144 GHz range. These signals originated from neither the GeCI" radical nor the GeC1÷ ion. The carrier of the spectrum seemed to be more stable than such transient species, as the spectrum was even observed in the dc discharge under sealed-off conditions. We considered GeC12 and GeC13 to be among the plausible candidates, and also GeHCI3, GeH2CI2, and GeH3C1, as hydrogen is easily supplied from water adsorbed on the surface of the sample cell. However, the observed spectrum was consistent neither with the reported lines of GeHC13 [21], nor with those of GeH3CI [22]. Similar clusters of strong signals were then observed in the frequency ranges near 147 and 151 GHz, which are shifted to high frequency by
M.J. Tsuchiya et al./Journal o f Molecular Structure 352/353 (1995) 407-415
3.8 and 7.6 GHz, respectively, from where the first spectrum was observed. The predicted spectral pattern based on the molecular structure of GeC12 from the electron diffraction study [2] accounted for the observation fairly well; R-branch transitions obeying b-type selection rules give rise to clusters repeated every 3.80 GHz, which corresponds to twice the C rotational constant. Three more series of clusters with similar patterns were soon identified, which were displaced from the first series by less than 1 GHz towards the high frequency. Three out of the four series found were assigned as originating from the abundant isotopic species, 74Ge35C12 (21.0%), 72Ge35C12 (15.7%), and 7°Ge35C12 (11.8%), of germanium dichloride in the ground state, on the basis of the isotopic relation between the rotational constants. The remaining series, which did not fit with the isotopic relation, was assigned to the spectrum in the u2 vibrational state of the most abundant species 74Ge35C12. Fig. 1 illustrates typical lines of 74Ge35C12 in the ground and u2 states, with K-type doubling caused by asymmetry. The component of the doublet corresponding to o d d values of K, + K~ (denoted as (co) in Fig. 1) is stronger than that with even values of Ka + Kc (00). The observed intensity ratio is consistent with the ratio 10:6 predicted
eo
oo
124578
X 3 I
124200
1242114
124408
124412 M H z
Fig. 2. Rotational transitions with resolved K-type doubling, 302,28 ~--293.27 and 303,28 ~--292,27 , of 74Ge35C12 in the ua (right) and u 3 (left) states. The intensity ratio of the K-doublet components for the Ul state is the same as those for the ground and u 2 states in Fig. 1, whereas for the u 3 state the ratio is reversed, i.e. (co): (oo) - 6: 10.
from the spin statistics of the chlorine, nucleus (I = 3/2), assuming Czv symmetry and an 1Al ground electronic state. Measurements of the weaker signals were carried out using the thermal reaction rather khan the discharge method. We finally observed more than one thousand signals originating from GeC12 in the frequency range 108-160 GHz. Some of them were assigned to the spectra of the higher vibrationally
Isotope
State
nrot
Jmaxa
Kmaxa
a (kHz) b
74Ge35C12
Ground ul v,2 u3 2u 2
84 30 86 28 61
38 32 41 32 39
6 4 5 4 5
23 16 25 14 22
72Ge35C12
Ground u2 2u2
48 60 24
38 41 32
6 5 5
t5 16 15
V°Ge3SCl2
Ground
44
38
6
12
76Ge35C12
Ground
29
32
5
12
I
124386
I111
e()
/o
124382
V~
e()
O0
eO
I
V3
Table 1 Profile of the data included in the least-squares analysis
(;rnund
V2
409
124582 M H z
Fig. 1. Rotational transitions with resolved K-type doubling. 302,28 -*--293.27 and 303,28 +-- 292,27, of 74Ge35C12 in the ground (right) and u2 (left) states. One c o m p o n e n t (denoted as co) of the K-type doublet is stronger than the other (oo) (see text), obeying the spin statistics for the chlorine nucleus. The observed line intensities are consistent with the calculated ratio of 10 : 6.
a M a x i m u m values of the rotational q u a n t u m numbers J and
Ko. b Standard deviation in the least-squares analysis.
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
410
Table 2 Observed microwave spectrum of 74Ge35C12 in the ground state Observed (MHz)
Rotational transition
O - Ca (kHz)
J'
K~,,
K~,,
J"
K~
K~'
28 28 27 27 26 26 25
0 1 2 1 2 3 3
28 28 26 26 24 24 22
27 27 26 26 25 25 24
1 0 1 2 3 2 4
27 27 25 25 23 23 21
109195.674 109195.674 109221.828 109221.828 109276.028 109295.415 109173.096
-14 -17 -260 b 55 b -58 -23 -122 b
29 29 28 28 27 27 26 25
0 1 2 1 2 3 3 5
29 29 27 27 25 25 23 21
28 28 27 27 26 26 25 24
1 0 1 2 3 2 4 4
28 28 26 26 24 24 22 20
113024.513 113024.513 113049.816 113049.816 113103.194 113113.797 113095.707 116791.104
-1 -2 -54 c 1094 -24 -39 -28 18
30 30 29 29 28 28 27
0 1 2 1 2 3 3
30 30 28 28 26 26 24
29 29 28 28 27 27 26
1 0 1 2 3 2 4
29 29 27 27 25 25 23
116853.138 116853.138 116877.621 116877.621 116928.996 116934.833 116974.286
17 17 394 124c -26 23 71
31 31 30 30 29 29 27
0 1 2 1 2 3 4
31 31 29 29 27 27 23
30 30 29 29 28 28 26
1 0 1 2 3 2 5
30 30 28 28 26 26 22
120681.517 120681.517 120705.150 120705.150 120754.214 120757.378 120019.849
17 17 -30 ¢ 144 19 46 3
32 32 31 31 30 30 28
0 1 2 1 2 3 4
32 32 30 30 28 28 24
31 31 30 30 29 29 27
1 0 1 2 3 2 5
31 31 29 29 27 27 23
124509.656 124509.656 124532.618 124532.618 124579.118 124580.796 124247.964
14 14 -13 10 24 12 52
34 34 33 33 32 32 31 31 30
0 1 2 1 2 3 4 3 5
34 34 32 32 30 30 28 28 26
33 33 32 32 31 31 30 30 29
1 0 1 2 3 2 3 4 4
33 33 31 31 29 29 27 27 25
132165.155 132165.155 132186.985 132186.985 132229.045 132229.045 132337.341 132315.491 132857.934
-30 -30 -14 -8 406 b -78 b -35 -99 b -140 b
Table 2 Continued Observed (MHz)
Rotational transition
O-C a (kHz)
J'
K~,~
K~¢.
J"
K'~
K~'
30 29
4 6
26 24
29 28
5 5
25 23
132287.079 137353.495
82 b 23
35 35 34 34 33 33 32 32 31 31 30 30
0 1 2 1 2 3 4 3 5 4 6 5
35 35 33 33 31 31 29 29 27 27 25 25
34 34 33 33 32 32 31 31 30 30 29 29
1 0 1 2 3 2 3 4 4 5 5 6
34 34 32 32 30 30 28 28 26 26 24 24
135992.546 135992.546 136013.849 136013.849 136053.444 136053.444 136149.290 136137.108 136531.770 136191.121 136668.526 134234.430
-22 -22 -28 -25 79 b -179 b 13 9 -33 120 b -61 32
36 36 35 35 34 34 33 33 32 32 31 31
0 1 2 1 2 3 4 3 5 4 6 5
36 36 34 34 32 32 30 30 28 28 26 26
35 35 34 34 33 33 32 32 31 31 30 30
1 0 1 2 3 2 3 4 4 5 5 6
35 35 33 33 31 31 29 29 27 27 25 25
139819.673 139819.673 139840.549 139840.549 139878.124 139878.124 139964.298 139957.526 140256.725 140055.542 142424.179 138908.784
-8 -8 18 20 704 -66 c -27 -35 -38 -13 6 -30
37 37 36 36 35 35 34 34 33 33 32 32
0 1 2 1 2 3 4 3 5 4 6 5
37 37 35 35 33 33 31 31 29 29 27 27
36 36 35 35 34 34 33 33 32 32 31 31
1 0 1 2 3 2 3 4 4 5 5 6
36 36 34 34 32 32 30 30 28 28 26 26
143646.533 143646.533 143666.997 143666.997 143702.663 143702.663 143781.409 143777.598 144014.261 143896.617 145512.955 143281.639
16 16 52 53 -17 c -884 24 -52 -53 -41 24 -33
38 38 37 37 36 36 35 35
0 1 2 1 2 3 4 3
38 38 36 36 34 34 32 32
37 37 36 36 35 35 34 34
1 0 1 2 3 2 3 4
37 37 35 35 33 33 31 31
147473.032 147473.032 147493.149 147493.149 147527.238 147527.238 147599.748 147597.713
-35 -35 42 42 244 -14 c -5 12
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415 Table 2 Continued Rotational transition
Observed (MHz)
s'
/~'o
~'c
s"
/C
/<'
34 34 33 33
5 4 6 5
30 30 28 28
33 33 32 32
4 5 5 6
29 29 27 27
0 - Ca (kHz)
411
frequencies, which are not presented in this paper, are available on request from the authors or the editorial office of the journal.l 4. Results and discussion
147792.477 147724.368 148840.413 147446.880
-14 82 68 25
a Observed frequency minus calculated frequency in kHz. b Blended lines, not used in the analysis. c Unresolved K-doublet, weighted with 0.625. d Unresolved K-doublet, weighted with 0.375.
excited states, vl, v3, and 2v2, as well as those of the minor isotopic species as 76Ge3SC12 (4.5%). Fig. 2 shows the signals assigned to the vl and v 3 states. In the case of the K-doublet component, the signals for the Vl state have the same intensity ratio as for the ground and v2 states. In contrast, the signals of the v3 state have the reverse ratio 6 : 10 for odd and even values of K~ + K,., because the v3 vibration is due to antisymmetric stretching and belongs to the b 2 symmetry species of the C2~ point group. The intensity ratio of the K-doublet components gave us the definitive assignment of the vibrational state. The intensities of the Vl and v 3 state lines were 2 0 - 3 0 % of those of the ground state lines, consistent with the vibrational frequencies. No hyperfine splittings due to the chlorine nuclear quadrupole were resolved for the lines observed in the present work. The transition frequencies measured in the present study were subjected to a least-squares fit, in which the effective Hamiltonian in Watson's A-reduced form [23], including the quartic centrifugal distortion constants, was used. Table 1 summarizes the profile of the data included in the analysis, where nrot is the number of observed rotational transitions, and Jmax and Kmax are the largest J and/Ca values covered, respectively. The spectra of minor isotopic species, involving 73Ge and 37C1, were excluded from the analysis, because of weak intensities and for the sake of simplicity. The observed frequencies of the main species 74Ge35C12 in the ground vibrational state are listed in Table 2 with their assignments and the o b s e r v e d - calculated ( O - C) values. Tables of
4.1. Equilibrium molecular structure The molecular constants of various isotopic species obtained by least-squares analysis are summarized in Table 3. For the 74Ge3SClz and 72Ge35C12 species, the molecular constants of the four (v l, V2, 2u2, and v3) and two (V2 and 2u2) vibrationally excited states, respectively, were derived, as well as those of the ground state. The uncertainties in parentheses correspond to one standard deviation of the fit. In some cases, the centrifugal distortion constants /Sj and 6K were fixed to the values in the ground or v2 s~ate. The inertia defects calculated from the observed rotational constants are also given in Table 3. The rotational constants of the V4Ge35C12 and 72Ge35C12 species were fitted to the formula B,, = Be - .iB(vl q- 1/2) - c~g(v2 + 1/2) - o~B(v3 q- 1/2) + "yB2(l,2 --~ 1/2) 2
(1)
The vibration-rotation constants % (v = 1, 2, and 3) and "Y22are given in Table 4 with their uncertainties corresponding to one standard devialtion. The c~2 and 722 values behave as expected for the two isotopic species. The equilibrium rotational constants derived by Eq. (1) are summarized in Table 5 together with the inertia defect calculated from these constants. As discussed in our previous paper [24] and the references cited therein [25-28], the rotational constants derived from the A-reduced form Hamil~onian are slightly different from the values corresponding to the real equilibrium structure. We made corrections corresponding to causes (2) and (3) in Ref. [24], using the centrifugal distortion constants calculated from the harmonic force field in Table 8. However, cause (4), the effect of electron orbital motion coupled with molecular rotation, was
i Data deposited with BLLD as Supplementary Publication number SUP26522 (21 pages).
412
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
Table 3 Molecular constants and inertia defect of germanium dichloridea Constant
A B C As Aj~ AK 6j t5K
74Ge35C12
Unit
Ground
vl
v2
v3
2v2
7229.653(13) 2613.0356(24) 1916.07269(42)
7231.873(83) 2604.1902(32) 1913.9420(11)
7291.478(42) 2609.0548(57) 1911.75535(43)
7197.727(63) 2610.2424(44) 1909.7690(12)
7354.093(26) 2605.1122(24) 1907.43491(45)
1.21882(64) -7.367(26) 38.46(47) 0.45234(fix) 1.834(fix)
1.19796(17) --8.096(10) 44.66(18) 0.4407(fix) 1.916(fix)
kHz kHz kHz kHz kHz
2.23628(65)
u A2
1.2254(12) --7.674(45) 37.89(46) 0.45234(63) 1.834(31)
A
1.22960(59) -7.890(34) 39.44(46) 0.45234(fix) 1.834(fix)
0.44725(59)
Constant
A B C Aj ASK AK ~g 6K A
1.1999(66) --7.62(10) 41.7(17) 0.4407(33) 1.916(96)
0.10542(111)
1.34053(90)
72Ge35C12
0.80083(102) 7°Ge35C12
76Ge35C12
MHz MHz MHz
Unit
Ground
/-'2
2u2
Ground
Ground
7327.383(25) 2612.9953(39) 1922.87028(79)
7390.037(28) 2609.0402(19) 1918.52667(30)
7453.067(69) 2605.1186(34) 1914.1785(10)
7430.472(22) 2612.9749(37) 1929.90755(67)
7137.378(35) 2613.0636(47) 1909.4958(10)
1.2207(21) --7.834(36) 40.35(57) 0.4468(11) 1.801(32)
1.20587(11) --7.8829(73) 44.18 (18) 0.4407(fix) 1.916(fiX)
1.20199(54) --8.568(27) 49.61 (71 ) 0.4407(fix) 1.916(fiX)
1.2254(19) --8.148(29) 41.81 (49) 0.44588(99) 1.760(26)
1.21514(52) --7.324(21) 38.20(35) 0.45234(fix) 1.834(fiX)
kHz kHz kHz kHz kH z
1.33081(62)
2.21593(97)
0.44121(71)
0.45404(86)
u A2
0.44420(74)
MHz MHz MHz
a la uncertainties in the unit of the last digit are in parentheses.
d i s r e g a r d e d , since the r o t a t i o n a l g values o f G e C I 2 have n o t been r e p o r t e d . T h e c o r r e c t e d e q u i l i b r i u m r o t a t i o n a l c o n s t a n t s a n d inertia defect Table 4 Vibration-rotation constants of germanium dichloride in MHza 74Ge35C12 ~1
72Ge35C12 v2
~3
//2
a n -2.220(84) -61.035(131) 31.926(64) -62.278(120) c~B 8.8454(40) 4.0190(179) 2.7932(50) 3.9886(102) c~c 2.1307(12) 4.3142(16) 6.3037(13) 4.3391(21) 7n 7B 3'c
-
0.395(44)
-
0.0191(59)
-
0.188(46)
0.0168(32)
-0.00155(53)
-
-0.00228(70)
a hr uncertainties in the unit of the last digit are in parentheses.
are c o m p a r e d in T a b l e 5 with the u n c o r r e c t e d values. In b o t h cases, the inertia defect has a small negative value, as is often the case for a p l a n a r t r i a t o m i c molecule. The c o r r e c t e d value Ae = - 0 . 0 0 4 7 5 ( 1 4 4 ) u A 2 is slightly larger in the a b s o l u t e value t h a n the u n c o r r e c t e d one, the difference c o r r e s p o n d i n g to the effect o f centrifugal d i s t o r t i o n . The residual inertia defect m a y be a t t r i b u t e d to the electronic t e r m Aelec due to the r o t a t i o n a l g values, a n d the higher o r d e r v i b r a t i o n - r o t a t i o n c o n s t a n t s neglected in this analysis. T h e b o n d length r e a n d b o n d angle 0e were calc u l a t e d f r o m the c o r r e c t e d e q u i l i b r i u m m o m e n t s o f inertia. T h r e e different sets o f values are derived f r o m the c o m b i n a t i o n s o f the m o m e n t s , which slightly differ f r o m each o t h e r because o f the
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415 Table 5 Equilibrium structure of germanium dichloride a Equilibrium rotational constants b Ae 7213.890 4- 0.083 MHz Be 2620.8596 ± 0.0103 MHz Ce 1192.4474 + 0.0016 MHz Inertia defect 2x~ -0.00272 4- 0.00143 u / k 2 Corrected equilibrium rotational constants c A~ 7213.879 ± 0.083 MHz Be 2620.8515 4- 0.0103 MHz Ce 1922.4570 ± 0.0017 MHz Inertia defect A~ -0.00475 ± 0.00144 u/~2 Bond length d (1~, Ib) 2.1694670 + 0.0000052 ,~ (In, Ic) 2.1694513 ± 0.0000033/~ (Ib, I,.) 2.1694365 4- 0.0000040 ,~ Average 2.1694516/~ Bond angle d
(la, lb) (I~, Ic) (lb, 4) Average
99.88212 99.88142 99.88403 99.88252
+ 0.00050 ° ± 0.00051 ° + 0.00060 ° °
a Errors correspond to 1a. Derived from the data of 74Ge35C12. b Derived from the constants in the Watson's A-reduced form Hamiltonian. c Corrected for the centrifugal distortion constants (see text). d Derived from the corrected equilibrium constants.
finite equilibrium inertia defect. The average values of the three sets are
413
and the harmonic force field in Table 8 as r z = 2 . 1 7 3 0 1 4 ( 6 ) /k and 0 z = 9 9 . 9 8 6 3 ( 6 ) °. The structural parameters given by the electron diffraction study [2] are r a = 2 . 1 8 3 ( 4 ) /~ and 0a = 100.3(4) °. The ra value is considerably larger than rz and r e. The r0 structure of CC12 is r 0 - 1 . 7 1 5 7 ( 2 8 ) /k and 00 = 109.2(3) ° [11], and the equilibrium structure of SiC12 is r e = 2 . 0 6 5 3 1 0 ( 2 6 ) • and 0e = 101.3240(16) ° [16]. The bond length of GeC12 is longer than those of CC12 and SiCI2 by 0.4537 A and 0.1041 A, respectively. For these homologous molecules, the bond length increases almost linearly with covalent bond radius, The bond angle of GeCI 2 is smaller than those of CC12 and SIC12 by 9.3 and 1.44 °, respectively. 4.2. Intramolecular f o r c e field
The inertia defect of 74Ge35C12 in the ground state and its vibrational changes are summarized in Table 6. The squared Coriolis coupling constants (~13)2 listed in Table 6 were calculated from the vibrational changes, where we used the u 1 and u2 vibrational frequencies from Raman spectroscopy [5] and the u 3 value from IR spectroscopy [4]. The (¢J3) c 2 values derived from the inertia defects in the u I and u 3 states are about 9% larger than the values from u2 and 2u2, the differences probably being ascribable to uncertainties in the Table 6 Inertia defects and squared Coriolis coupling constants a
r e = 2.169452 4-0.000015/~ 0e = 99.882 5 4- 0.001 5 ° where the uncertainties are estimated from the discrepancies. The molecular structures determined by the recent ab initio calculations, re = 2.177 A and 0e -- 100.35 ° [7], r e = 2.191 /k and 0e = 100.5 ° at the M R S D C I level [8], and r e = 2.182 /k and 0e = 99.95 ° at the MP2 L A N D L 1 D Z * level [9], agree well with the present equilibrium values; the discrepancies are at most 1.0 and 0.6%, respectively, for the bond length and bond angle. The r z structure w a s calculated from the rotational constants in the ground state of 74Ge35C12
Inertia defect Ground 0.44725 5:0.00059 u A 2 Change from the ground state value uI -0.34183 -t- 0.00126 u •2 u2 0.89328 ± 0.00108 u/]2 u3 0.35358 + 0.00118 u A 2 2u 2 1.78903 + 0.00088 u A 2 Squared Coriolis coupling constants (~3) 2 uI 0.15213 4- 0.00056 u2 0.13923 4- 0.00104 u3 0.15231 ± 0.00051 2u 2 0.13804 5:0.00043 Average 0.14568 b a Errors correspond to 1cr. Derived from the data of 74Ge35C12. b Averaged value of the vl and v2 states.
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
414
Table 7 Centrifugal distortion constants of 74Ge35C12 in kHz Constants As
Asx AK ~j t~K
7"aaaa ~-bbbb ~-~ ~'1 72 ATe
Observed a 1.2482(90) -7.945(181) 34.61(252) 0.4625(47) 1.762(155) --111.65(1011) --8.6928(521) --1.2928(521) 16.802(732) 1.676(149)
Calculated b 1.290 -7.535 36.37 0.469 1.947 --120.5 --8.913 -1.409 14.66 1.24
observed values. The Coriolis coupling constants ((~3) 2 calculated for the 74Ge35C12 and 72Ge35C12 species are 0.146 and 0.151, respectively. The av constants of the 74Ge35C12 species listed in Table 4 were subjected to the analysis to determine the third-order anharmonic force constants, following the procedure described by Kuchitsu and Morino [30]. The definition of the anharmonic force constants is Vanh = (1/6)frrr(Ar ~ q-
+ (1/2)frr~'(Arl + Ar2)ArlAr2 + (1/2)frro(Ar 2 +
-0.012(215)
The equilibrium values, la uncertainties are in parentheses. b Calculated from the harmonic force constants in Table 8. c KirchhotVs ~- planarity defect.
Ar~) Ar~)AO +fr/oArl Ar2AO
+ (1/2)froo(Arl + Ar2)AO 2 + ( 1 / 6 ) J ~ 0 0 A 0 3
(2)
a
reported vibrational frequencies. If we assume the energy difference between ul and u3 to be smaller than the literature value [4,5] by 2 cm -l, the ((~3) 2 values derived from the u 1 and u3 states agree with those from the u2 and 2u2 states. The ((~3) 2 values for the 72Ge35C12 species, 0.145 7(9) and 0.146 4(6), derived from the inertia defects in the u 2 and 2u 2 states, respectively, are similar to the corresponding values for the normal species. Equilibrium centrifugal distortion constants in the A-reduced form are calculated by applying Eq. (1) and the results are summarized in Table 7 for the 74Ge35C12 species. The "rxxxx (x = a,b, c) constants are calculated from the equilibrium values of A j, A j/c, A/(, and 6j, and the -q term from A s and As/( , as shown in Table 7. The planarity defect by Kirchhoff [29], A T = -0.012(215) kHz, is essentially zero, as expected for the equilibrium constants of a planar molecule. The squared Coriolis coupling constant was combined with the fundamental vibrational frequencies to determine the harmonic force field. The resulting harmonic force constants are listed in Table 8. The uncertainties in the harmonic force constants reflect the uncertainties in the squared Coriolis coupling constant ( ~ 5%) and the vibrational frequencies ( ~ 1%). The centrifugal distortion constants calculated from the harmonic force constants are compared in Table 7 with the
The harmonic force field was fixed as above. The determined constants are given in Table 8 with errors estimated from uncertainties in the av constants. Table 8 also lists the cubic potential constants kill, etc., for the 74Ge35C12 species. The oQ constants calculated for the 72Ge35C12 species, Table 8 Force constants of germanium dichloride GeCI2
SiCI2a
GeF2 b
Unit
1.7321 A 97.17 deg
re 0e
2.16945(2) 99.8825(15)
2.06531(3) 101.3240(16)
fr f~e frO
2.066(34) 0.232(34) --0.010(55) 0.90(17)
2.535(23) 0.278(23) 0.120(2) 1.053(2)
4.08 0.26 --0.01 0.96
mdyn A -1 mdyn A -j mdyn mdyn A
-8.95(35) -0.102(35) 0.078(96) -0.266(53) -0.685(90) -2.321(95)
-11.75(15) -0.208(20) -0.389(17) -0.464(13) -1.129(23) -2.826(14)
-22.65 -0.26 -0.07 -0.36 -0.81 -2.23
mdyn A -2 mdyn A 2 mdyn A -1 mdyn A l mdyn mdyn A
-13.499(76) -11.876(26) 3.04(11) -4.599(8) -58.80(49) 0.157(23)
-23.90 -9.23 8.42 -7.37 -77.53 1.06
cm -1
)Co f~rr frr/ frro f~e0 fro0
fooo
kill c -10.27(12) ktl 2 k122
-5.67(12) 3.496(14) kz22 -3.8613(15) kl33 -37.49(40) k233 0.65(14)
a Ref. [16]. b Ref. [17]. c For main isotopic species.
c m -1 ~3.1-1
cm
1
cm- 1 cm- 1
M.J. Tsuchiya et al./Journal of Molecular Structure 352/353 (1995) 407-415
a A = - 6 1 . 8 MHz, a~ = 4.0 MHz, and a c = 4.3 MHz, reproduce well the observed values listed in Table 4. In Table 8, the harmonic and anharmonic force constants of GeCI2 were compared with those of SiCI 2 [16] and GeF2 [17]. The stretching force constants fr and frrr of GeC12 are much weaker (by about 20% and 50-60%, respectively) than those of SiC12 and G e F 2, corresponding to the longer bond length (by about 5 and 25%). The fro constant of SiCI 2 is positive, whereas those for GeCI2 and GeF2 are essentially zero. The bending force constants fo and fooo are smaller (by about 15%) than those of SiCI 2, but almost equal to those of GeF2.
Acknowledgments We thank the Kurata Science Foundation, Itoh Science Foundation, and Iketani Science Foundation, for financial support. Calculations for the present study were carried out at the Computer Center of Kyushu University.
References [1] K. Tanaka, M.J. Tsuchiya and H. Honjou, in preparation. [2] Gy. Schultz, J. Tremmel and I. Hargittai, J. Mol. Struct., 55 (1979) 207. [3] L. Andrews and D.L. Frederick, J. Am. Chem. Soc., 92 (1970) 775. [4] J.H. Miller and L. Andrews, J. Mol. Struct., 77 (1981) 65. [5] I.R. Beattie and R.O. Perry, J. Chem. Soc. (A), (1970) 2429. [6] G.A. Ozin and A.V. Voet, J. Chem. Phys., 56 (1972) 4768.
415
[7] J.M. Coffin, T.P. Hamilton, P. Pulay and I. Hargittai, Inorg. Chem., 28 (1989) 4092. [8] M. Benavides-Garcia and K. Balasubramanian, J. Chem. Phys., 97 (1992) 7537. [9] J. Karolczak, Q. Zhuo, D.J. Clouthier, W.M. Davis and J.D. Goddard, J. Chem. Phys., 98 (1993) 60. [10] A. Charo and F.C. DeLucia, J. Mol. Spectrosc., 94 (1982) 363. [11] M. Fujitake and E. Hirota, J. Chem. Phys., 91 (1989) 3426. [12] H. Shoji, T. Tanaka and E. Hirota, J. Mol. Spectrosc., 47 (1973) 268. [13] V.M. Rao, R.F. Curl, Jr., P.L. Timms and J.L. Margrave, J. Chem. Phys., 43 (1965) 2557. [14] V.M. Rao and R.F. Curl, Jr., J. Chem. Phys , 45 (1966) 2032. [15] M. Tanimoto, H. Takeo, C. Matsumura, M. Fujitake and E. Hirota, J. Chem. Phys., 91 (1989) 2106. [16] M. Fujitake and E. Hirota, Spectrochim. Acta., Part A, 59 (1994) 1345. [17] H. Takeo, R.F. Curl, Jr. and P.W. Wilson, J. Mol. Spectrosc., 38 (1971) 464. [18] H. Takeo and R.F. Curl, Jr., J. Mol. Spectrosc., 43 (1972) 21. [19] K. Tanaka, T. Okabayashi and T. Tanaka, J. Mol. Spectrosc., 132 (1988) 476. [20] T. Tanaka, K. Kato, T. Okabayashi and K. Tanaka, Rev. Sci, Instrum., 60 (1988) 106. [21] P. Venkateswarlu, R.C. Mockler and W. Gordy, J. Chem. Phys., 21 (1953) 1713. [22] J. Demaison, G. Woldarczak and J. Burie, J. Mol. Spectrosc., 140 (1990) 322. [23] J.K.G. Watson, J. Chem. Phys., 46 (1967) 1935. [24] K. Miyazaki, M. Tanoura, K. Tanaka and T. Tanaka, J. Mol. Spectrosc., 116 (1986) 435. [25] J.K.G. Watson, Mol. Phys., 15 (1968) 479. [26] E.B. Wilson, Jr. and J.B. Haword, J. Chem. Phys., 4 (1936) 260. [27] D. Kivelson and E.B. Wilson, Jr., J. Chem. Phys., 20 (1952) 1575. [28] T. Oka and Y. Morino, J. Mol. Spectrosc., 6 (1961) 472. [29] W.H. Kirchhoff, J. Mol. Spectrosc., 41 (1972) 333. [30] K. Kuchitsu and Y. Morino, Bull. Chem. Soc. Jpn., 38 (1965) 814.