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Infrared photochemical reaction of C2F3 C1 induced by a tea CO2 laser
Volume
INFRARED
PHOTOCHEMICAL
15 April 1979
CHEWCAL PHYSICS LETTERS
62, number 3
REACTION
Keiichi NAGAI, Mikio KATAYAMA,
OF C,F,CI
INDUCED
BY A TEA CO2 LASER
Hitoshi MIKUNI and Makoto TAKAHASI
Department of Pure and Applied Sciences, CoIlege Komaba. Meguro-ku. Tokyo 1.53. Japan
of
General Education.
nte Utziversity of Tok_vo
Received 9 January 1979
An infrared photochemical reaction of CzF,Cl induced by a TEA CO? hser was observed. &lainreaction products were C2F, and ClFC=CFCI(tzrcns). bemg quite different from those obtained by thermal or ultraviolet photochemical reactions.
I_ Introduction
2. Experimental
The development of high power infrared lasers has increased interest in Investigations of infrared photochemical reactions. Reaction products obtained by irradiation with infrared lasers were often identical with those of thermal or ultraviolet photochemical reactions, but several papers have reported a specific effect of infrared radiation, in contrast with simple heating [I-3] _ In the present study we have observed the infrared photoreaction induced by a TEA CO, laser in gaseous C,F$I which strongly absorbs the CO, laser irradiation in the 9.6 pm region. Recently, Letokhov et al_ [4,53 observed the spectrum of a dielectric breakdown radiation emitted from C,F,Cl under Iaser irradiation in the 10.6 pm band as well as the spectrum of the strongest luminescence excited by 9.6 pm radiation, and found that both spectra were identical_ Furthermore, they identified the lines of the F atom and of C? and C12* ions or the C2 radical [4,5] _ In the present experiment, the reaction products were examined by infrared absorption and mass spectra, and it was found that the major products of the infrared photochemical reaction Induced by the 9.6 pm laser pulse were C2F4 and ClFC=CFCl(trans).These compounds differ entirely from those produced by uItravioIet photochemical or thermal reaction of gaseous C2F3Cl.
The TEA CO, laser which we used for the present experiment is the same as the one described in previous papers [6,7] _ The oscillation of the 9.6 pm band was accomplished by introducing I50 torr of SF6 gas into a small cell in the laser cavity. The power output was slightly less tian I J. By reducing its pressure in the cell, simultaneous oscillations of the 10.6 ,um R band and the 9.6 pm band were also obtained, and their intensities depended upon the pressure of the gas. Two types of cylindrical reaction cell made of duralmine were used. One had dimensions of 10 cm length and 30 mm diameter, and the other was 5 cm in length and 20 mm diameter. Both ends of the cells were closed with KC1 plates. The sample gas in the reaction cell was irradiated by the laser pulse focused with a germanium lens off = 5 cm_ For the identification of products an infrared absorption spectrum and a mass spectrum of the products were observed after laser irradiation for about 30 minutes- No appreciable differences in products were found with changing cell dimensions. Most of the experiments were performed at l-10 torr and under laser irradiation of moderate intensity. Under these conditions the absorption of multiple photons takes the first step of the infrared photochemical reaction_ Furthermore, measurements at a pressure of about 100 torr were also performed by irradiating higher laser power, where the production of quite different compounds was observed_ The reaction in this case was -499
Volume 62, number 3
CHEMICAL
mainly promoted by an av&nche duced by dielectric breakdown_
of electrons
PHYSICS LETTERS
pro-
3_ Results ?he P( I 6) line of the 9-6 urn bmd of the CO, I=r coincides with the P branch of the v, band of C,F,Cl_ The weak absorption is also observed at the R branch of the IO.6 pm Iaser- When the sample gas of CzF3Cl in the reaction cell at a pressure of I-IO WC was irndiated by the focused T&4 CO, laser of the 9.6 ,um band, the !uminescence was unobservedpresumably because the luminescence threshold is higher at lower pressure of about 10 torr- Howevermeasurements of infrared absorption and mass spectra indicate that the Iaser irradiation produces severai kin-& of products_ The major products of the reaction, induced by the irradiation of the laser of about 30 mJ. were C,F, and ClFC=CFCl(trans) with almost equal concentration_ It should be noted that the anaSysis of the products by infrared absorption did not show any production of F~C=CC.I, or CIFC=CFCl(cis)_ Aithongh no reAction was induced by irradiation at IO.6 pm \~ith 500 mJ or by illumination at 9.6 pm with 3 mf respectiveIy, simultaneous irradiation at IO.6 pm with 500 mJ or by illuminascribed above promoted the reaction significantly.
A considerable observed,
enhancement
when the irradiation
of the reaction was also of 10.6pm
with 500
mJ was made 3 m after the iilumination of the 9.6 pm Zaser with 3 mJ_ We have observed very frequentiy that the infrared Iaser induced photoproduct is simiiar to that of the products by ultraviolet light and even to thermal reactions (71. However, the 9.6 pn> lmer induced reaction of C,F-$l is strikingly different from the resuits of the&l reaction and flash photolysis. Atkin and StedmJn [Sj observed that the products of the thermal reaction of CzF3Cl were tans- and cis-1,2_dichlorohesttfIuoro-cycIoburane m the temperature range of TOO-~00°C. At rarhcr higher temperature of 560°C, the products of thermal reaction also contain other components with moIecuIar weights higher than C,F,Ci [9]- On the other hand, the C, or C, compounds have never been found in the TEA CO? Iaser induced reaction products_ If the 9.6 pm laser irradiation produced 1 ,2-dichloro500
15 April 1979
hexafh.taro-cycIobutane 3s an intermediate reaction product, the decomposition of this moIecule by the infrared laser would give rise to the production of almost equal amounts of C,F, and ClFC=CFCI(trans). However, the following experiments eliminate the above mentioned mechanism of the 9.6 pm laser induced reaction of CzF3CL We synthesized pure 1,2dichIoro-hexafiuoro-cyciobutane by distilling the thermal reaction products of CzF$I at 210°C_ The cis and trans forms of this molecule have infrared absorptions at the waveiengths of 9.6 ltrm and IO.6 pm_ It was found that the irradiation of the 9.6 pm Iaser for 30 min produced C1F3CI and CzF4 with the ratio 7 I 3 from c4F&12, and 10.6 pm laser photoreaction gave rise to the production of C7F3CI and a trace of C2F4_ However_ the production of C’ICF=CFCl(trans) was not confirmed. The reaction yields were only 10% under the present experimental conditions_ These resuIts exclude the assumption that the 9.6 pm Jaser induced reaction of C,F3CI gives rise firstly to the production of C4F&Iz and its decomposi tion produces the final products. A flash photolysis investigation by Tyerman (IO] showed that CF, and CFCI were produced in 3 photochemical reaction of C,F,CI. We also examined the reaction products of ultraviolet photoreaction using 3 Xe flash with power output of about 2 kJ, and Found .that the main products were CF,CI and CF4, completely different from the infrared laser photochem
ical products. Tyerman also observed that the products of Rash photoIysis of a mixture of C,F,CI and Hz included H,CFCI. In order to find the difference between the f&h photoIysis and the infrared laser reaction, a mhlure of CzFSCl and ffz (4 torr : 6 torr) ~3s irradiated by the 9.6 pm laser and the reaction products were examined. The analysis of mass spectrum shows that the largest amount of substance produced is C2HF3 as shown in table 1. The infrared spectrum of the products indicates the existence ofC!,MF3, C7F+ C!,H?, H,C=CF, and HCI. These ex&imental results cZearly reveal thedifference between the reactions induced by the flash photolysis and the 9.6 pm laser_ Thus, it may be suggested from our observation that the initial process of the 9-6 pm laser photoresction is CzF3Cl -+ C,F, f CL The 9-6 pm laser induced reaction of a rmxture of propene, 3s a radical scavenger, and C,F3CI was also
Volume 62, number 3
Table 1 Relative concentrations of the 95 pm laser induced photochemical products determined by mass spectra. Reactant: mbture of CtF,Cl and Hz (4 torr : 6 torr). Laser powers: 15 mJ and 800 n-J Molecule
Reiari\epeak height
CzHz C2 HZ F2
C2HF3 C211ClF2 C2 F4
CzCI,F2
examined.
25 mJ
800 mJ
0.10 0.08 1.0 0.10 0.23 0.10
0.26 0.21 1.0 0.12 o-39 0.08
The presence of propene
and Nyman
[ 1 l]
observed
oxidation
of C,F,Cl,
CF,CICOF
in
illur&ating with light of wavelength longer thG 3000 A. Its reaction rate was so slow that it was necessary to irradiate the reactant for five days to get appreciable amount of product_ However, they confirmed that a trace of Cl radical increased the reaction rate significantly. The rapid reaction of the 9.6 pm laser induced photochemistry of the mixture appears to manifest the production of the Cl radicaI in the process of the infrared !aser induced reaction_ Hence, our results may support the assumption that the initial infrared photoreaction induced by the 9 -6 ,um laser is C, F;Cl + C,F, + CL Since the infnred laser photochemicaI reaction product of a mixture of C2F3C1 and 02, CF,ClCOF. has absorption at 10.6 pm, the 10.6I-lm laser irradiated CF,ClCOF gives rise to an increase in th& concentration of COF, and COFCl in the products, while the concentration of CF,CICOF decreases. photochemical
The irradiation of the IO.6 pm P lines of the TEA CO, laser with output of 1 J induced 250 breakdowns out of 1000 Iaser shots in gasews C,F,CI at 170 torr. The reaction products due to the breakdown were mzidy CF,CI and C, F4, which are completely different from tboze of the infrared photochemical reaction described above. The threshold power of the breakdown induced by the 10.6 pm R lines was SlightIy lower than that of the 10.6 Hrn P lines. This may be due to the fact that in gaseous C,F,CI the absorption coefficient of the R lines is Ia&er than that of the P lines.
4. Vibrational modes of C2F3C! photodissociatiori
did not affect
the production of C2F4, but CIFC=CFCl(trans) was not produced_ Provided that the propene molecule annihiIstes the Cl radical, it is reasonable that CIFC=CFCI(trans) was not found inthe present experiment. The 9.6 pm laser photoreaction of a mixture of C2 F,CI and 0, (4 torr : 6 torr) was also investigated, and it was found that the reaction was very rapid. The reaction products were CF,CICOF, COF, and a small amount of COFCl. in the flash photolysis experiment, Tyerman found the production of COF2 and CFClO, but nor of CF,CICOF [IO] _ However, HaszeIdine
15 April 1979
CHEMICAL PHYSICS LETTERS
and its infrared
The infrared absorption spectrum of C,F,CI has been observed by Mann et al. [ 12]_ The assignment of its fundamental vibrations relevant to the present investigation is Xsted in table 2_ The line centers of the P, Q and R branches of the v4 mode. a CF stretching vibration, are observed at 1052 cm-‘, 1058 cm-I and 1065 cm-’ respectively. A strong absorpticn of the second overtone of the vIo band (deformation vibration of CF?) is also observed at 1080 cm-‘. The vibration observed at around 4115 cm-’ (2~4 f v5 + w,, or 2~~ f vIo) is one of the combination bands which may be excited by a multiple step absorption of the 9.6 flrn laser_ The infrared laser dissociation of molecules was well understood by the assumption that the molecules are excited to the true continuum of the levels above the dissociation Iimit through excitation of the quasicontinuum of the vibrational levels [ 13]_ The lowest activation energy of cleavage of bonds in CT F3Cl moleTable 2 Fundamental vibration frequencies (in cm-‘)
of CzF3CI reie-
wnt to the present investigation [ 171
~-___
Designstton
Trequencl’
v3
WC “CF “CF
v4
“CF
vs “IO
TCl %F,
1792 1336 1215 IO58 689 538
Ul “2
501
Volume
62. number
3
CHEMICAL
PHYSICS
cuIe is that of the CCI bond and its energy is about 80 kcaI/mole [14,15] _ Under the present experimental conditions, almost 100 infrared photons interact with one C2F3CI molecufe, and the absorption of 35 infrared photons may be enough to dissociate the CC1 bond. Not only simultaneous irradiation of both lasers, 9.6 pm and 10.6 pm with power output of 4 mJ and 500 mJ respectively, but aIso 10.6 pm Iaser irradiation 3 cls after the irradiation of the 9.6 pm Iaser gives rise LO tie infrared photodecomposition of C2F3CI. This is because the lifetime of the V~ vibrational mode is a few w, and absorption of the 10.6 pm Iaser by the v4 vibrntionalIy excited molecules raises the moIecuIes to the dissociation limit. It may also be possible that the combination band observed at 2012 cm-l (v7 + v5) is excited by double photon absorption of 9.6 ym and 10.6 pm laser and further excitation from this band produces dissociation of the molecule. Our experimental results mentioned above may suggest that the initial process of 9.6 pm laser photoreaction is C2F3CI --t C2F3 + CL However, it remains unsolved why only the trans form of 1.SdichIorodifIuoro_ethyIene, but not the cis form and C12C=CF,. is produced. In conclusion, it is evident from the present experiment that the 9.6pm laser induced photoreaction of CzF3CI is totalIy different from the thermaI and uItmvio!et photochemical reactions_
LETTERS
15 April 1979
Acknowledgement This research was supported partly by the Grantin-Aide from the Ministry of Education of Japan_
References [1 1 N-G. B-v,
E.P. Markin, AN OmevskiI, A-V. Pankratov and AM. Skachkov. JETP Letters 14 (1971) 165 [2] J-L_ Lyman and RJ. Jensen. Chem- Phys_ Letters 13 (1972) 42J. 131 A_ Yogev, R.MJ. Lowenstein and D. Amar. J. Am. Chem_ Sot. 94 (1972) 109I[41 V-S_ Letokhov, EA- Ry-nbov and 0-A. Tumanov. Soviet Phys. JETP 36 (1973) 1069. [5J R.V. Ambutzumhn. N.V. Cheksiin. VS. Letokhov and E-A_ Ryabov. Chem. Phys- Letters 36 (1975) 301. [61 K_ Nz& ;Lnd M. ICacay~~~n, Cfiem. Phys. Letters 51 (1977) 329. (71 K. Nagi and i%LKatayyarna, Bull_ Chem. Sot. Japan. to be pubIished_ 181 B_ Atkin and bf. Stedman, J.. CIIem. Sot. (1962) 512. [9] W-T_ &fiIler. U.S. Patent 2.733.277 (Jan. 31. 1956). [IO] BJ.R_Tyerman. Chem. Commun- (1968) 39X [ 1 I J R-N_ Haszeldine and F. Nymn, J_ Chem. Sot. (1959) 1084. [ I21 D-E. hfann, N. Acquists and E.R. Plyler. J. Chem- Phys210953) 1049(131 J-G. Bhck. E. Yablonovitch, N. Bloembergen and S. XutimeI. Phys. Rev. Letters 38 (1977) 1131_ [ I41 WV_Braub and W. Tsans. Chem- Phyr Letters 44 (1976) 3.54. [ 151 L. p~uling. The nature of the chemical bond (Cornell Univ- Press, Ithaca, 1960).
INFRARED
PHOTOCHEMICAL
15 April 1979
CHEWCAL PHYSICS LETTERS
62, number 3
REACTION
Keiichi NAGAI, Mikio KATAYAMA,
OF C,F,CI
INDUCED
BY A TEA CO2 LASER
Hitoshi MIKUNI and Makoto TAKAHASI
Department of Pure and Applied Sciences, CoIlege Komaba. Meguro-ku. Tokyo 1.53. Japan
of
General Education.
nte Utziversity of Tok_vo
Received 9 January 1979
An infrared photochemical reaction of CzF,Cl induced by a TEA CO? hser was observed. &lainreaction products were C2F, and ClFC=CFCI(tzrcns). bemg quite different from those obtained by thermal or ultraviolet photochemical reactions.
I_ Introduction
2. Experimental
The development of high power infrared lasers has increased interest in Investigations of infrared photochemical reactions. Reaction products obtained by irradiation with infrared lasers were often identical with those of thermal or ultraviolet photochemical reactions, but several papers have reported a specific effect of infrared radiation, in contrast with simple heating [I-3] _ In the present study we have observed the infrared photoreaction induced by a TEA CO, laser in gaseous C,F$I which strongly absorbs the CO, laser irradiation in the 9.6 pm region. Recently, Letokhov et al_ [4,53 observed the spectrum of a dielectric breakdown radiation emitted from C,F,Cl under Iaser irradiation in the 10.6 pm band as well as the spectrum of the strongest luminescence excited by 9.6 pm radiation, and found that both spectra were identical_ Furthermore, they identified the lines of the F atom and of C? and C12* ions or the C2 radical [4,5] _ In the present experiment, the reaction products were examined by infrared absorption and mass spectra, and it was found that the major products of the infrared photochemical reaction Induced by the 9.6 pm laser pulse were C2F4 and ClFC=CFCl(trans).These compounds differ entirely from those produced by uItravioIet photochemical or thermal reaction of gaseous C2F3Cl.
The TEA CO, laser which we used for the present experiment is the same as the one described in previous papers [6,7] _ The oscillation of the 9.6 pm band was accomplished by introducing I50 torr of SF6 gas into a small cell in the laser cavity. The power output was slightly less tian I J. By reducing its pressure in the cell, simultaneous oscillations of the 10.6 ,um R band and the 9.6 pm band were also obtained, and their intensities depended upon the pressure of the gas. Two types of cylindrical reaction cell made of duralmine were used. One had dimensions of 10 cm length and 30 mm diameter, and the other was 5 cm in length and 20 mm diameter. Both ends of the cells were closed with KC1 plates. The sample gas in the reaction cell was irradiated by the laser pulse focused with a germanium lens off = 5 cm_ For the identification of products an infrared absorption spectrum and a mass spectrum of the products were observed after laser irradiation for about 30 minutes- No appreciable differences in products were found with changing cell dimensions. Most of the experiments were performed at l-10 torr and under laser irradiation of moderate intensity. Under these conditions the absorption of multiple photons takes the first step of the infrared photochemical reaction_ Furthermore, measurements at a pressure of about 100 torr were also performed by irradiating higher laser power, where the production of quite different compounds was observed_ The reaction in this case was -499
Volume 62, number 3
CHEMICAL
mainly promoted by an av&nche duced by dielectric breakdown_
of electrons
PHYSICS LETTERS
pro-
3_ Results ?he P( I 6) line of the 9-6 urn bmd of the CO, I=r coincides with the P branch of the v, band of C,F,Cl_ The weak absorption is also observed at the R branch of the IO.6 pm Iaser- When the sample gas of CzF3Cl in the reaction cell at a pressure of I-IO WC was irndiated by the focused T&4 CO, laser of the 9.6 ,um band, the !uminescence was unobservedpresumably because the luminescence threshold is higher at lower pressure of about 10 torr- Howevermeasurements of infrared absorption and mass spectra indicate that the Iaser irradiation produces severai kin-& of products_ The major products of the reaction, induced by the irradiation of the laser of about 30 mJ. were C,F, and ClFC=CFCl(trans) with almost equal concentration_ It should be noted that the anaSysis of the products by infrared absorption did not show any production of F~C=CC.I, or CIFC=CFCl(cis)_ Aithongh no reAction was induced by irradiation at IO.6 pm \~ith 500 mJ or by illumination at 9.6 pm with 3 mf respectiveIy, simultaneous irradiation at IO.6 pm with 500 mJ or by illuminascribed above promoted the reaction significantly.
A considerable observed,
enhancement
when the irradiation
of the reaction was also of 10.6pm
with 500
mJ was made 3 m after the iilumination of the 9.6 pm Zaser with 3 mJ_ We have observed very frequentiy that the infrared Iaser induced photoproduct is simiiar to that of the products by ultraviolet light and even to thermal reactions (71. However, the 9.6 pn> lmer induced reaction of C,F-$l is strikingly different from the resuits of the&l reaction and flash photolysis. Atkin and StedmJn [Sj observed that the products of the thermal reaction of CzF3Cl were tans- and cis-1,2_dichlorohesttfIuoro-cycIoburane m the temperature range of TOO-~00°C. At rarhcr higher temperature of 560°C, the products of thermal reaction also contain other components with moIecuIar weights higher than C,F,Ci [9]- On the other hand, the C, or C, compounds have never been found in the TEA CO? Iaser induced reaction products_ If the 9.6 pm laser irradiation produced 1 ,2-dichloro500
15 April 1979
hexafh.taro-cycIobutane 3s an intermediate reaction product, the decomposition of this moIecule by the infrared laser would give rise to the production of almost equal amounts of C,F, and ClFC=CFCI(trans). However, the following experiments eliminate the above mentioned mechanism of the 9.6 pm laser induced reaction of CzF3CL We synthesized pure 1,2dichIoro-hexafiuoro-cyciobutane by distilling the thermal reaction products of CzF$I at 210°C_ The cis and trans forms of this molecule have infrared absorptions at the waveiengths of 9.6 ltrm and IO.6 pm_ It was found that the irradiation of the 9.6 pm Iaser for 30 min produced C1F3CI and CzF4 with the ratio 7 I 3 from c4F&12, and 10.6 pm laser photoreaction gave rise to the production of C7F3CI and a trace of C2F4_ However_ the production of C’ICF=CFCl(trans) was not confirmed. The reaction yields were only 10% under the present experimental conditions_ These resuIts exclude the assumption that the 9.6 pm Jaser induced reaction of C,F3CI gives rise firstly to the production of C4F&Iz and its decomposi tion produces the final products. A flash photolysis investigation by Tyerman (IO] showed that CF, and CFCI were produced in 3 photochemical reaction of C,F,CI. We also examined the reaction products of ultraviolet photoreaction using 3 Xe flash with power output of about 2 kJ, and Found .that the main products were CF,CI and CF4, completely different from the infrared laser photochem
ical products. Tyerman also observed that the products of Rash photoIysis of a mixture of C,F,CI and Hz included H,CFCI. In order to find the difference between the f&h photoIysis and the infrared laser reaction, a mhlure of CzFSCl and ffz (4 torr : 6 torr) ~3s irradiated by the 9.6 pm laser and the reaction products were examined. The analysis of mass spectrum shows that the largest amount of substance produced is C2HF3 as shown in table 1. The infrared spectrum of the products indicates the existence ofC!,MF3, C7F+ C!,H?, H,C=CF, and HCI. These ex&imental results cZearly reveal thedifference between the reactions induced by the flash photolysis and the 9.6 pm laser_ Thus, it may be suggested from our observation that the initial process of the 9-6 pm laser photoresction is CzF3Cl -+ C,F, f CL The 9-6 pm laser induced reaction of a rmxture of propene, 3s a radical scavenger, and C,F3CI was also
Volume 62, number 3
Table 1 Relative concentrations of the 95 pm laser induced photochemical products determined by mass spectra. Reactant: mbture of CtF,Cl and Hz (4 torr : 6 torr). Laser powers: 15 mJ and 800 n-J Molecule
Reiari\epeak height
CzHz C2 HZ F2
C2HF3 C211ClF2 C2 F4
CzCI,F2
examined.
25 mJ
800 mJ
0.10 0.08 1.0 0.10 0.23 0.10
0.26 0.21 1.0 0.12 o-39 0.08
The presence of propene
and Nyman
[ 1 l]
observed
oxidation
of C,F,Cl,
CF,CICOF
in
illur&ating with light of wavelength longer thG 3000 A. Its reaction rate was so slow that it was necessary to irradiate the reactant for five days to get appreciable amount of product_ However, they confirmed that a trace of Cl radical increased the reaction rate significantly. The rapid reaction of the 9.6 pm laser induced photochemistry of the mixture appears to manifest the production of the Cl radicaI in the process of the infrared !aser induced reaction_ Hence, our results may support the assumption that the initial infrared photoreaction induced by the 9 -6 ,um laser is C, F;Cl + C,F, + CL Since the infnred laser photochemicaI reaction product of a mixture of C2F3C1 and 02, CF,ClCOF. has absorption at 10.6 pm, the 10.6I-lm laser irradiated CF,ClCOF gives rise to an increase in th& concentration of COF, and COFCl in the products, while the concentration of CF,CICOF decreases. photochemical
The irradiation of the IO.6 pm P lines of the TEA CO, laser with output of 1 J induced 250 breakdowns out of 1000 Iaser shots in gasews C,F,CI at 170 torr. The reaction products due to the breakdown were mzidy CF,CI and C, F4, which are completely different from tboze of the infrared photochemical reaction described above. The threshold power of the breakdown induced by the 10.6 pm R lines was SlightIy lower than that of the 10.6 Hrn P lines. This may be due to the fact that in gaseous C,F,CI the absorption coefficient of the R lines is Ia&er than that of the P lines.
4. Vibrational modes of C2F3C! photodissociatiori
did not affect
the production of C2F4, but CIFC=CFCl(trans) was not produced_ Provided that the propene molecule annihiIstes the Cl radical, it is reasonable that CIFC=CFCI(trans) was not found inthe present experiment. The 9.6 pm laser photoreaction of a mixture of C2 F,CI and 0, (4 torr : 6 torr) was also investigated, and it was found that the reaction was very rapid. The reaction products were CF,CICOF, COF, and a small amount of COFCl. in the flash photolysis experiment, Tyerman found the production of COF2 and CFClO, but nor of CF,CICOF [IO] _ However, HaszeIdine
15 April 1979
CHEMICAL PHYSICS LETTERS
and its infrared
The infrared absorption spectrum of C,F,CI has been observed by Mann et al. [ 12]_ The assignment of its fundamental vibrations relevant to the present investigation is Xsted in table 2_ The line centers of the P, Q and R branches of the v4 mode. a CF stretching vibration, are observed at 1052 cm-‘, 1058 cm-I and 1065 cm-’ respectively. A strong absorpticn of the second overtone of the vIo band (deformation vibration of CF?) is also observed at 1080 cm-‘. The vibration observed at around 4115 cm-’ (2~4 f v5 + w,, or 2~~ f vIo) is one of the combination bands which may be excited by a multiple step absorption of the 9.6 flrn laser_ The infrared laser dissociation of molecules was well understood by the assumption that the molecules are excited to the true continuum of the levels above the dissociation Iimit through excitation of the quasicontinuum of the vibrational levels [ 13]_ The lowest activation energy of cleavage of bonds in CT F3Cl moleTable 2 Fundamental vibration frequencies (in cm-‘)
of CzF3CI reie-
wnt to the present investigation [ 171
~-___
Designstton
Trequencl’
v3
WC “CF “CF
v4
“CF
vs “IO
TCl %F,
1792 1336 1215 IO58 689 538
Ul “2
501
Volume
62. number
3
CHEMICAL
PHYSICS
cuIe is that of the CCI bond and its energy is about 80 kcaI/mole [14,15] _ Under the present experimental conditions, almost 100 infrared photons interact with one C2F3CI molecufe, and the absorption of 35 infrared photons may be enough to dissociate the CC1 bond. Not only simultaneous irradiation of both lasers, 9.6 pm and 10.6 pm with power output of 4 mJ and 500 mJ respectively, but aIso 10.6 pm Iaser irradiation 3 cls after the irradiation of the 9.6 pm Iaser gives rise LO tie infrared photodecomposition of C2F3CI. This is because the lifetime of the V~ vibrational mode is a few w, and absorption of the 10.6 pm Iaser by the v4 vibrntionalIy excited molecules raises the moIecuIes to the dissociation limit. It may also be possible that the combination band observed at 2012 cm-l (v7 + v5) is excited by double photon absorption of 9.6 ym and 10.6 pm laser and further excitation from this band produces dissociation of the molecule. Our experimental results mentioned above may suggest that the initial process of 9.6 pm laser photoreaction is C2F3CI --t C2F3 + CL However, it remains unsolved why only the trans form of 1.SdichIorodifIuoro_ethyIene, but not the cis form and C12C=CF,. is produced. In conclusion, it is evident from the present experiment that the 9.6pm laser induced photoreaction of CzF3CI is totalIy different from the thermaI and uItmvio!et photochemical reactions_
LETTERS
15 April 1979
Acknowledgement This research was supported partly by the Grantin-Aide from the Ministry of Education of Japan_
References [1 1 N-G. B-v,
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