Thermal Decomposition of CF3Cl

Abstract

The unimolecular decomposition CF3C1 + Kr -CF3 + C1 + Kr has been studied using two different techniques, atomic resonance absorption spectrometry (ARAS) and laser schlieren (LS) density gradients, in two laboratories. As in our previous joint investigation of C C 4 dissociation, the ARAS and LS techniques give completely consistent results over the overlapping temperature range, 1800-2200 K. The title reaction is found to be fairly close to the low-pressure limit. The ARAS measurements between 1521 and 2173 K give k2nd = 1.73 x IO-' exp(-33837K/T) cm3 molecule-' s-l ( f 2 7 % at lo). This is in good agreement with the earlier ARAS measurements of b g e r and Wagner. k2nd = 1.15 x exp(-28330K/T) cm3 molecule-' s-' ( f 2 0 % at l o ) is obtained from the LS results between 1800 and 3000 K. The good agreement between methods verifies both the C-C1 fission path for the CFX1 dissociation and the curve-of-growth used in the C1 atom ARAS analysis. RRKM analysis of these rate data indicated a larger than usual magnitude for hEdown, in agreement with our previous findings on CC4, but here it was necessary that it increase with T.The best fit was with = 270 cm-'. The RRKM fit to the data is given by the three-parameter expression k2nd = 2.95 x 1024T8.50 exp(-48133K/7') cm3 molecule-' s-l for a pressure of 300 Torr. This final expression agrees with both the ARAS and LS results to within f 2 5 % and can be used in modeling applications between 1500 and 3000 K. IntroductionC1 atom ARAS,8 and we can also compare with these results.

Vibrational relaxation and dissociation in the perfluoromethyl halides, CF3Cl, CF3Br, andCF3I

“…Our results on CF 3 Cl dissociation were published earlier [10], but are partially reiterated here for comparison and further evaluation. An important new feature of the CF 3 I (and CF 3 Br) experiments is the detection and modeling of secondary reactions, primarily the combination 2CF 3 : C 2 F 6 .…”

“…The model for CF 3 Cl is given in ref. [10]. To minimize the number of adjustable parameters in these calculations, the dissociation barriers, E 0 , of these bond fissions were taken as the JANAF (18) , and the transition states, which gov-0 ⌬H 0 ern the HPL rate, were described by a restricted-rotor Gorin model [12].…”

“…An important new feature of the CF 3 I (and CF 3 Br) experiments is the detection and modeling of secondary reactions, primarily the combination 2CF 3 : C 2 F 6 . A version of the secondary kinetic mechanism derived from this modeling was cited and used in the earlier CF 3 Cl article [10].…”

On the heats of formation of trifluoromethyl radical CF3 and its cation CF3+

“…Recently, Kumaran et al 14 inferred D 0 ͑CF 3 ϪI͒ϭ55.0 kcal/mol ͑55.6 kcal/ mol at 298 K͒, which implies ⌬H f 298 ‫ؠ‬ ͑CF 3 ͒ϭϪ110.7 kcal/ mol, and therefore supports Tsang's value for ⌬H f ‫ؠ‬ ͑CF 3 ͒. In a subsequent paper, Kumaran et al 15 report D 0 ͑CF 3 ϪCl͒ϭ89.0Ϯ1.5 kcal/mol ͑89.9Ϯ1.5 kcal/mol at 298 K͒, significantly higher than their previous inference 6, 16 of 84.8 kcal/mol, and implying ⌬H f 298 ‫ؠ‬ ͑CF 3 ͒ϭϪ108.3Ϯ1.7 kcal/mol. However, after elaborate comparison with data on other halomethanes and high-quality ab initio calculations, Kumaran et al 15 conclude that although the experimental D 0 ͑CF 3 ϪCl͒ fits very well in the trends for the remaining experimental bond strengths, the JANAF 6 value for ⌬H f ‫ؠ‬ ͑CF 3 ͒ is nevertheless probably correct, and that most inconsistencies can be resolved by attaching error bars which are somewhat larger than those originally quoted.…”

Thermal Decomposition Studies of Halogenated Organic Compounds

“…[ls], CH3Cl [10,11], C3H3Cl [19], CFC13 [16,20], CF2C12 [16,21], CF3Cl [16,22], CF2HCl [13], CF3I [12], CH3I [23], C2H5I [24], C6H5I [25], and CC120 [26]. The methods used are nearly identical in all cases, and for the purposes of discussion, we will illustrate the method with CH3I data -ln(IdIo) (It and Io refer to transmitted and incident I-atom resonance light intensities, respectively), is measured as CH3I decomposes.…”