J. Phys. Chem. 1992, 96, 6504-6508
6504
(16) Bertie, J. E.; Jacobs, S.M.J . Chem. Phys. 1977, 67, 2445. (17) The 'electronvolt per molecule" unit is commonly used in the astro-
nomical community. Useful conversion factors to other units of radiation dose are 1 eV molecule-' = 536 Mrad = 5.36 MGy. (18) (a) Kitta, K.; Kritschmer, W. Astron. Astrophys. 1986,122, 105. (b) Tielens, A. G. G. M.;Hagen, W.; Greenberg, J. M. J. Phys. Chem. 1983.87, 4220. (19) Golecki, I.; Jaccard, C. J . Glaciol. 1978, 21, 247. (20) (a) Strauulla, G.; Leto, G.; Baratta, G. A.; Spinella, F. J . Geophys. Res. 1991. 96. 17.457. (b) Baratta. G. A.: Leto. G.:. SDinella. . F.:. Strazzulla. . G.; Foti, G. Astron. Asjrophys. 1991, 252, 421: (21) Eiben, K.; Taub, I. A. Nature 1967, 216, 782. (22) Box, H. C. Radiation Effects: ESR and ENDOR Analysis; Academic: New York, 1977; p 161;(23) For example, see: (a) Ghormley, J. A.; Stewart, A. C. J . Am. Chem. SOC.1956, 78, 2934. (b) Kroh, J.; Green, B. C.; Spinks, J. W. T. Can. J . Chem. 1%2,40,413. (c) Draganic, Z. D.; Vujosevic, S.;Negron-Mendoza, A.; Azamar, J. A,; Draganic, I. G. J . Mol. Euol. 1985, 22, 175. (24) (a) Swallow, A. J. Radiation Chemistry; John Wiley: New York, 1973; pp 142, 155. (b) Buxton, G . V. In Radiation Chemistry; Farhataziz,
Rodgers, M.A. J., Eds.;VCH Publishers: New York, 1987; pp 326-327. (c) Spinks, J. W. T.; Woods, R. J. An. Introduction to Radiation Chemistry, 3rd ed.; John Wiley: New York, 1990; pp 263-264. (25) Magee, J. L.; Chatterjee, A. J. Phys. Chem. 1980.84, 3529. (26) (a) Fontana, B. J. J. Chem. Phys. 1959, 31, 148. (b) See also: Windsor, M.W. Fifth InternationalSymposium on Free Radicals; University of Uppsala: Uppsala, Sweden, 1961; p 73-1. (27) (a) Jackson, J. L. J . Chem. Phys. 1959, 32, 154. (b) Jackson, J. L. J. Chem. Phys. 1959, 31, 722. (28) Schutte, W. A.; Greenberg, J. M.Astron. Astrophys. 1991,244, 190. (29) Flournoy, J. M.; Baum, L. H.; Siegel, S.J. Chem. Phys. 1962, 36, 2229. (30) Sugisaki, M.;Suga, H.; Seki, S.In Physics of Ice; Riehl, N., Bullemer, B., Engelhardt, H., Eds.; Plenum: New York, 1969; p 329. (31) (a) Siegel, S.; Baum, L. H.;Skolnik, S.;Floumoy, J. M. J. Chem. Phys. 1960,32,1249. (b) Siegel, S.; Floumoy, J. M.; Baum, L. H. J. Chem. Phys. 1961, 34, 1782. (32) Wu, 2.;Gillis, H. A.; Klassen, N. V.; Teather, G. G. J . Chem. Phys. 1983, 78, 2449. (33) Johnson, R.E. J . Geophys. Res. 1991, 96, 17, 553.
Red Emission in Chemically Produced Excited Oxygen Flow. 1. Attribution of the Emission Spectrum to CuCI, Toshihiko Tokudat and Nobuyuki Fujii* Department of Chemistry, Nagaoka University of Technology, Nagaoka 940- 21, Japan (Received: September 4, 1991; In Final Form: April 7, 1992)
Earlier observation of red chemiluminescence obtained by exposing heated copper to a chemically produced singlet oxygen flow was reproduced in a gas-phase reaction by mixing copper chloride vapor with singlet oxygen. This paper gives an identification of the emitter. The low-resolution spectrum of the red emission showed some progressions. They had a band spacing of 360 cm-I, which was identical with that of the symmetric vibrational stretching of the ground electronic state of CuC12. The band intensity was calculated assuming that the emitter is CuC12 and at least a part of the observed spectrum is well explained. We thus attribute the red emission observed previously to the %,, 211r transition in CuC12.
-
Introduction
Recently, Yoshida et al.' have observed a strong red chemiluminescence by exposing heated copper to a flow of excited oxygen produced via the chemical reaction 2NaOH
+ H 2 0 2+ C12
-
OJA)
+ 2NaCl+ 2 H 2 0 (1)
where unreacted chlorine and water vapor represent less than a few percent. Subsequently, some researchers observed the same emission using several metals?+ The experimental results of those researchers are that the emission spectrum was identical with the metals used and also that chlorine greatly enhanced the red emission. Accordingly, it has been claimed that the heated metals played a catalytic role in producing the emitter. Huang et a1.2 have related the emission enhancement to refreshment of the catalyst by chlorine because of the volatility of copper chloride. Although a definite assignment could not be made from the spectra, Zhuang et al.3have discussed the possibility of the emitter being a compound of oxygen and chlorine, such as CIO, C102, and C1202,and give the CIC1-00 stretching mode of 359 cm-l as most probable. Bacis et al.4 reported nearly identical experimental results. In our preliminary report,5we gave further reasons to suppose that CuC12is responsible for the red emission. The proposal was deduced from the following experimental results: (1) Copper chloride deposition was observed on the reaction tube along the red emission tail when the heated metallic copper was placed in the chemically produced excited oxygen flow. (2) The emission Present address: Technical Research and Development Institute, Japan Defense Agency, 2-2-1, Nakameguro, Meguro-ku, Tokyo 153 Japan.
intensities from copper were extremely strong relative to those from other metals. (3) The same emission due to copper chloride (produced by reaction of C12with copper compounds present as impurities in some metals) or due to copper chloride contaminating the thermocouple, the heater, etc. was observed even when no copper compound was present in the flow. (4) The previous experiment in which the red emission was obtained by mixing copper chloride vapor with the excited oxygen flow suggests that the chemiluminescence reaction is not catalytic. We also reported that the red emission was always accompanied by a strong near-infrared emission and concluded that the emitter may be CuCl, from the infrared spectrum analysk6 Although spectroscopic studies for CuCl have been widely performed and the emission understood in detail, the spectrmpic data for CuC12 are poor. Emission data for CuC12 are absent, except for the far-infrared region.' Absorption results show that CuC12 has peaks at 19000 and at 9000 cm-1.8-11Accordingly, we consider it important to clarify spectroscopically the identity of the present emitter. In the present study, we analyze the visible emission spectrum and simulate the distribution of the band intensity of the emission spectrum due to excited CuC12. Experimental Seetion
The excited oxygen flow system was analogous to that used for a chemical oxygen-iodine laser.12 It was constructed of a singlet oxygen generator, a water vapor trap, a reaction tube including a copper chloride vapor injector, and a high pumping speed vacuum system. The apparatus is made of poly(viny1 chloride) except for the vapor trap tube and the reaction tube. The pressure was measured with an MKS Baratron capacitance manometer
0022-3654/92/2096-6504$03 .OO/O 0 1992 American Chemical Society
The Journal of Physical Chemistry, Vol. 96, No. 15, 1992 6505
Red Emission in Excited Oxygen Flow
Flow
000 I
Reentry trap
Rotary oil "ml P P
25% NaOH solution
system
I,
multiplier
c12
Figure 1. Schematic diagram of the present flow system.
..
,
.
.'
Vapor
Nichroie Wire Ceramic Coat Figure 2. Schematic diagram of the vapor injection device.
(Type 122A). Figure 1 shows a schematic diagram of the flow system. The reaction solution, which contained 8 dm3of 35 wt 5% H202 (Junsei Chemical Co., Ltd.) and 3 dm3 of 25 wt 5% NaOH (Nacalai), was mixed in the singlet oxygen generator, 200 X 300 mm2 square and 200 mm high. The chlorine bubbler, which was i.d. on the sides, made of Teflon tube with many pores of OS-" was submerged about 10 mm below the surface of the solution. The chlorine (Sumitomo Seika Inc., 99% purity) was introduced into the reaction solution through the bubbler at an average flow rate of 1 mmol/s. The production of singlet oxygen is roughly proportional to the amount of chlorine passed, so the total flow rate of oxygen was about 1 mmol/s and the operational pressure in the reaction tube was about 0.5 Torr. The temperature of the solution was kept at about -15 OC throughout the experiment. As the reaction progressed, the activity of the solution diminished and there was a gradual increase in the quantity of unreacted chlorine flowing out from the generator, but no other products were generated. The water vapor evaporated into the oxygen flow was removed by a water vapor trap cooled at -78 OC with a dry ice and methanol mixture. A vapor injection device for copper dichloride is depicted schematically in Figure 2. The powder cell of IO-" diameter and its cap were made of Pyrex glass. The cell was surrounded by a nickel-chromium wire heater and coated with ceramics. The vapor was ejected through pores about 1 mm in diameter. Here, we took great care that metallic parts such as the thermocouple and electric wire were not in contact with the 0 2 ( l A ) flow, by covering them with glass wool. The cell was placed upstream of the 02(lA) inlet of the reaction tube, 70 mm in diameter. CuCl, powder (Nacalai, 95% purity) was placed in the device prior to the experiment. The amount of copper chloride vapor was controlled by the heater temperature.
[80
&a
E2
buI
6M
navelength
€a103
(nml
122
E&
im
m
1(0
IEO
iu
m
MI
Wavelength (nm)
Figure 3. Red chemiluminescent spectrum observed by mixing copper chloride vapor with singlet oxygen flow. The resolution is 0.3 nm/ channel. The classification of the bands is explained in the text.
Spectra were taken with a silica optical fiber and a 0.25-m spectrometer with 300 or 1200 grooves/mm grating blazed at 500 nm (Ritsu Inc.) and a spectral multichannel analyzer (SMA) with 512 active channels (IRY/par-G/R, Princeton Inst. Inc.).
Results and Discussion 1. Measurement of the Emission Spectrum. We obtained reproducible spectroscopic data over a wide range of wavelength using the SMA. Figure 3 shows the low-resolution spectrum of the red emission measured by SMA with 0.3-nm/channel resolution. The spectrum is basically identical with that shown in our previous reports.s After correction for the detector response, we found that the strongest peak in the spectrum is at 691 nm. The band heads shown in Figure 3 have regular energy spacings, about 160-200 cm-l on the blue side and 360 em-l on the red side. The energy spacing on the blue side is suggested to be formed from different progressions. However, we found that the 360-cm-' spacing also exists between heads on the blue side. Here, we labeled this progression as the first series, as shown in Figure 3. The other strong band heads on the blue side also formed a series, which we labeled as the second series. We found yet another series of small heads in the spectrum and we labeled these as the third series. The band-head wavenumbers, and the spacing between them, are shown in Table I. The energy spacings within each series were almost equal to 360 em-'(Eli - El,, - E2,, and Eji - Ev in Table I). As we pointed out in the previous report,s the magnitude of 360 cm-' corresponds to the symmetric stretching vibrational energy of the electronic ground state of C U C ~ ~ . ~Absorption *~O studies8J0concerning the upper electronic state for CuCI2indicate only an absorption peak at 19 000 cm-', which is insufficient to explain our experimental results.
6506 The Journal of Physical Chemistry, Vol. 96, No. 15, 1992
Tokuda and Fujii
TABLE I: Summary of Band Heads and Energy Spacing ( c d ) '
first series AE EI
E I I - E I , El,-E2, 179 353 191 352 199 413 176 36 1 148 359 149 362
second series AE E2n-Elj 174 161 214 184 21 1 213
E2 16121 (620) 15756 (635) 15396 (650) 15006 (666) 14673 (682) 14313 (699)
E > - E2,
E>-E3,
third series
AE E3,- Elr
E3
E3,-E3,
Eli- E?,
E?, - El,
365 360 390 90 333
243 85 275
360
80
367
14916 (670) 14589 (685) 14233 (703) 13840 (723)
266 327
94 233
355
126 230
393
132 26 1 106
364 36 1 369 365
174
193
36 1
85
259
359
247
115
" The wavelengths in nanometers are given in parentheses. TABLE II: Summary of Spectroscopic Constants for Band Intensity Calculrtioas of CuCI2'
J
112 211s 312 22g+ 112 2A8 512 '4 312
'IIS 670
680
690
7cO
710
720
Wavelength (nm)
Figure 4. High-resolutionspectrum. The resolution is 0.07 nmlchanncl.
In order to get more information about the spectrum structure of the emitter, we measured a higher resolution spectrum of the red emission using a 1200 grooves/mm grating. The red emission spectrum thus obtained is shown in Figure 4. The spectrum is very diffuse, but we found some obvious peaks of 10-20-cm-' spacing on each band. These spacings could not be assigned to a rotational structure because there are more bands observed than there ought to be rotational branches in a 211-211 transition and their profile does not correspond to usual P(Q)R branches. The observed splitting cannot be attributed solely to the isotope effect either, because the relative abundance of isotope molecules does not correspond to the relative peak intensities. It would seem more reasonable to assign this splitting to a different vibrational mode, such as the bending vibration, but at present there is insufficient data contained in the high-resolution spectrum to confirm this. 2. CdcuLtioa of tbe Emission Band Intensity of Cpc12. Recently, Bauschlicher et al.I3 reported the electronic structure for CuC12 calculated theoretically by the coupled-pair functional method and showed that the spectrmpic constants thus obtained were in good agreement with the experimental values. We basically employed those theoretical values for the calculation of the red emission band intensity. Not all the constants required for the calculation were given in the theoretical paper, so we estimated unknown constants as follows. We adopted identical values for the vibrational frequencies and intermolecular distances in the two components of the 2& state, i.e., 211g(1/2)and 2&(3/2). We took the asymmetric stretching and bending vibrational constants in the ligand field states to be the same as those of the ground state. These two vibrations affect the prediction of the band wavelength as described later. Also,we introduced Bauschlicher
re, A
T,, symmetric asymmetric cm-l stretch stretch bend Ligand Field States
2.056 2.056b 2.091 2.108 2.1Ogb
0 178 1576 7514 9656
357 35Ib 358 352 352b
499 499c 499c 499c 499c
101 l0lC l0lC lOlC lOlC
360"
8V
Charge-Transfer State 211u 112, 312 2.194
16686
265
"These values are based on the results of ref 13. bThesame values for the splitting electronic states. CThesame value of the ground state. "Estimated value in ref 13 by assuming no coupling of the stretches. cEstimatcd value by following the reduction of the vibrational energy between the ligand field state and the charge-transfer state. et al.'s13 estimate of 360 cm-I as the asymmetricvibrational energy in the charge-transfer state (which assumes no coupling of the stretches) and 80 cm-l for the bending mode, which was estimated from 101 cm-l given for the same mode in the 211gstate, assuming proportionality between the fundamental vibrational energy of the ligand field state and the charge-transfer state. The spectroscopic constants employed are summarized in Table 11. Transitions from the three lowest electronic excited states of CuC1, [2Zg+,2Ag(3/2), 2Ag(5/2)] to the ground state are all forbidden because of the Laporte rule for electric dipole radiation. However, the transition from the charge-transfer state, 211u,to the lower states is fully allowed. Accordingly, we mainly considered the transition from this state. The calculation procedure of the band intensity of CuClz emission was performed as follow^.^^-'^ The difference of the internuclear distance between the upper and lower electronic state was converted into that of the normal coordinate. Then, assuming that the vibrational wave functions are those of harmonic oscillators, Franck-Condon factors were evaluated by the calculation of overlap integrals for each of the normal coordinates. Finally, the band intensity was calculated assuming the Boltzmann distribution on the vibrational levels of the upper electronic state. 3. Comparisoa of the Relative Bad Intensity. Given that the SMA can record only 120 nm in a single spectrum and the
The Journal of Physical Chemistry, Vol. 96, No. 15, 1992 6507
Red Emission in Excited Oxygen Flow
NAM-ENGTH (nnl
NAVELENGTH
Figure 5. Comparison of the calculated and the measured distribution of band intensities. Marks are the observed ones (see text). Solid vertical
-
lines are calculated for the 211u
211,(1/2) transition.
-
-
-
the distribution for the 211u
emission extends from 580 to 820 nm, we recorded the emission in three parts, centered at 650, 700, and 750 nm. These three recordings are indicated by symbols 0, A, and 0,respectively, in Figure 5 , which compares the measured intensities with ,IIU - 2& intensities for CuC12,given by solid vertical lines. Calculated intensities are given only by bands with v‘ = 0 because of significantly low intensity due to other transitions (v’ > 0), at Boltzmann equilibrium. The calculated maximum peak (v” = 6) has been set equal to the observed one at 695 nm. Both band intensities agree well within the scatter of different experimental measurements. Accordingly, we attributed the observed fmt series to the radiative transition from the 211ustate to the ground electronic state of CuCl,. The band heads of the second series are red-shifted by about 174 cm-’(Eli- E2) or blueshifted by about 193 cm-’ (E2 - E l j ) from the fmt series,as shown in Table I. Since the energy spacing of 360 cm-l in the second series is basically identical with that of the first series, it could be considered that the second series is a progression due to emission from 211uto levels that are a combination of the symmetric stretching vibration with other vibrational modes of the ground electronic state of CuC1,. However, the emission intensity distribution is not easily explained in that way. Although the spectral features are analogous to those of the first series, the band heads of the second series disappeared from the spectrum in the red region. Second, if the population of the upper state is vibrationally in thermal equilibrium, the emission intensity should be smaller than that of the first series. For these reasons we consider that the second series does not arise from transitions including the bending or asymmetric stretching mode. Bauschlicher et al.I3 reported that the effects of spin-orbit coupling on the electronic energy levels of CuC12 could not be neglected and the 2Zg+and ’II, states are close in energy? They calculated that the spin-orbit components of the ,IIg state are separated by 178 cm-I. This value is in good agreement with the difference between the first and second series of about 174 or 193 cm-’ as shown in Table I. Vibrational constants for the two components of the 2& state are probably very similar. Moreover, we assumed that the spin-orbit splitting in the upper state (not calculated in ref 13) is zero. This will mainly change the absolute value of calculated band wavelength. So the calculated band intensity for the transition from the zIIu to the ,II,(3/2) state is shown by the symbol 0 in Figure 6, together with the transition 211u ,I4(1/2) (ground state) shown by vertical lines. It seems that the calculated progression of the 211u 211,(3/2) transition is in good agreement with the second series with respect to the wavelength. However, the relative intensity between the progressions of zIIg(1 /2) and %,(3/2) transitions did not agree with the observed spectrum shown in Figure 3. In addition, the observed spectrum has no progression on the red side except the first series. We calculated theoretical intensity distributions for 211u 211 (3/2) on the basis of overlap integrals. The influence of the difference in internuclear distance between the two states involved
-
-
-
-
Inn1
Figure 6. Distribution of calculated band intensities for the 211u 211,(3/2) transition and variation of the spectral feature with the internuclear distance: 0, Are = 0; A, +0.005; 0,+0.01 A. Vertical lines are 211g(1/2) transition.
WAVELENGTH
(nm)
-
Figure 7. Distribution of calculated band intensities for the 211u %+,
-
transition are shown by dotted lines. Solid lines are the distribution for the 211u 211,(1/2) transition. in the band intensity distribution is shown in Figure 6. The calculated maximum band position moves to the shorter wavelength as the difference in internuclear distance Are is decreased, as shown by the symbols A and in Figure 6. The best match to observation appears to correspond to Are = +0.01 A. Also, we calculated the band intensity for the allowed ,Eg+transition. The result is shown by broken lines in Figure 7. The calculated progressions seem to correspond to bands observed on the red side of the experimental spectrum, although the band positions do not correspond exactly. It is noticed that the bands on the red side of the observed spectrum are wider than those on the blue side. This large bandwidth suggests the overlap of several bands. Considering the inaccuracy in the calculation arising from the anharmonic oscillator, it is reasonable to assume that at least part of the band series on the red side originates from the 211u 9,+ transition. We found that the regular spacing of about 250 cm-’ was present between the third and some of the second series and also between the first and third series as shown in Table I. This value is in good agreement with the theoretical symmetric stretch frequency of 265 cm-’ for the ,IIUstate,’j but no reasonable assumption can be made to attribute the origin of the third series. The splitting of 20 cm-’of every band observed in high resolution is close to the difference between the fundamental bending vibrations of the upper and lower electronic states: Aw2 = ob; wb; = 101-80 cm-I. For vibrational thermal equilibrium in the upper state, the spectrum should have its strongest subband at the blue side of every band head, while the observed subband maximum intensity is shifted toward the band center. This could be due to a nonequilibrium population of vibrational levels in the upper electronic state 211u. Indeed as 0 2 ( ’ A ) is the energy donor in the excitation of CuCl,, it is possible that the population of excited CuClz has a nonequilibrium vibrational distribution. Moreover the structure of the upper electronic state is not known. Some nonlinearity in this upper electronic state might be the cause
-
-
Tokuda and Fujii
6508 The Journal of Physical Chemistry, Vol. 96, No. 15, 1992
I
900
HAVELENGTH (nm)
Figure 8. Distribution of calculated band intensities of the allowed transition from *nuto *Ag states in the near-infrared region.
3 WAVELENGTH (nn)
Figure 9. Distribution of calculated band intensities of the forbidden transitions from 2Ag to 211g+states in the near-infrared region.
of a change in intensity distribution, for example. In a previous wort6 we reported that the near-infrared emission with three peaks at 1.1, 1.3, and 1.5 pm was observed with the red emission. In addition, the higher resolution spectrumsrecorded around the peak at 1.3 pm showed several subbands whose spacing was analogous to that observed in the visible spectrum. The transitions from the ,Ifuto ,$(5/2) and ,$(3/2) states of CuC12 correspond to the near-infrared emission, and these are the allowed transitions. The calculated band intensity in the near-infrared region is shown in Figure 8. The calculated spectrum shows only two progressions, whereas the observed spectrum shows three peaks. If the forbidden transition ,Ag 211rof CuC12is considered, the band spectra calculated under the usual selection rule are reported in Figure 9. Their progressions are not very close to the observed infrared spectrum either. The emission due to this forbidden transition can be observed easily when the emitter concentration is high. The states, 2$(5/2) and 2$(3/2), of CuCl, are close in energy to O2('A). Then it seems that there is a possibility of a resonant energy transfer process from OZ('A) to C U C I ~ ( ~ Aperhaps ~), followed by a second energy transfer to C U C I ~ ( ~ Agiving ~ ) , the C U C ~ ~ ( excitation. ~II~)
-
Conclusion The red emission observed in the action of chemically produced singlet oxygen on heated copper is obtained by mixing copper chlorine vapor with a chemically produced singlet oxygen flow. The observed spectrum was classified into three band series. The band spacing in each series was 360 cm-I, in agreement with the symmetric vibrational stretching of the ground electronic state of CuC12. In addition, we observed on a higher resolution spectrum a series of subbands separated by about 20 cm-' in energy, attributed to the difference in the bending modes of the 211uand 2nostates. On the basis of the spectroscopic constants calculated by Bauschlicher et al., the band intensity of CuClz emission using the Franck-Condon principle was calculated. The observed visible emission is close to the calculated results, and we suggest that the red emission is due to the zIIu ,II,(1/2), QU ,ng(3/2), and ,nu zZg+transitions. We also calculated the allowed transitions from 211uto ,$(5/2) and 2$(3/2) states and the forbidden transition from the '$ state to the ground state zIIs of CuCl,. From the comparison of the calculated emission intensities with observed ones, we suggest that both transitions are believed to contribute the near-infrared emission observed in a previous work. Acknowledgment. We would like to express our thanks to Dr. H. Itou for helpful discussions and valuable comments and also to K. Kobayashi and Y.Amako for assistance with some of the experiments. The present work was in part supported by a Grant-in-Aid of Scientific Research from Ministry of Education, Science and Culture, Japan.
-
-
-
References and Notes (1) Yoshida, S.; Tokuda, T.; Shimizu, K. Appl. Phys. Lett. 1989,55,2707. (2) Huang, R.; Zhang, R.; Zare, R. N. Chem. Phys. Lett. 1990,170,437. (3) Zhuang, Qi.; Cui, T.-J.; Xie, X.-B.; Sang, F.-T.; Yuan, Q.-N.; Zhang, R.-Y.; Yang, H.-P.; Li, Li.; Zhu, Q.-S.; Zhang, C.-H. Proc. SPIE-Inr. Soc. Opt. Eng. 1990,1397, 157. (4) Bacis, R.; Bonnet, J.; Bouvier, A. J.; Churassy, S.; Grozet, P.; Erba,
B.; Georges, E.; Jouvet, C.; Lamarre, J.; Louvet, Y.; Nota, M.; Pigache, D.; Ross, A. J.; Setra, M. Proc. SPIE-Int. Soc. Opt. Eng. 1990, 1397, 173. ( 5 ) Tokuda, T.; Fujii, N.; Yoshida, S.; Shimizu, K.; Tanaka, I. Chem. Phys. Lett. 1990, 174, 385. (6) Yoshida, S.; Tokuda, T.; Shimizu, K.; Ogasawara, K.; Sawano, T. Appl. Phys. Lett. 1990, 57, 645. (7) VanLiere, M.; DeVore, T. C. High Temp. Sei. 1984, 18, 185. (8) Hougen, J. T.; Leroi, G. E.; James, T. C. J . Chem. Phys. 1961, 34, 1670. (9) Lcroi, G. E.; James, T. C.; Hougen, J. T.; Klemperer, W. J . Chem. Phys. 1962, 36,2879. (10) DeKwk, C. W.; Gruen,D. M. J . Chem. Phys. 1966,44,4387. (1 1) DeKock. C. W.: Gruen. D. M. J . Chem. Phvs. 1968.49.4521. (12) S h i h ; K.; Sawano, T.; Tokuda, T.; Yoshida, S.; Tanaka,'I. J. Appl. Phys. 1990,69, 79. (13) Bauschlicher, C. W., Jr.; Roos, B. 0.J . Chem. Phys. 1989,91,4785. (14) Herzberg, G.Molecular Spectru and Moleculur Structure; D. van Nostrand: New York, 1966; Vol. 111, Electronic Spectra and Electronic
Structure of Polyatomic Molecules, Chapter 2. (15) Herzberg, G. Molecular Spectra and Molecular Structure; D. van Nostrand: New York, 1968; Vol. 11, Infrared and Raman Spectra of Polyatomic Molecules, Chapter 2. (16) Wilson, E. B., Jr.; Decius, J. C.; Cross, P. C. Moleculur Vibrations, The Theow of Infrured and Ramun Vibrational Soectru: McGraw Hill: New York, 1955; chapter 1.
