UNIMOLECULAR REACTION AND COLLISIONAL DEACTIVATION OF CHEMICALLY ACTIVATED 1,2-DIFLUOROETHANE PRODUCED BY MERCURY PHOTOSENSITIZATION OF CHLOROFLUOROMETHANE AT 300 DEGREES K AND 475 DEGREES K

The mercury photosensitization of CH2CIF mixed with 10% propene was used as a source of CH2F radicals for the generation of chemically activated 1,2-C2H4F2*. The pressure required for stabilization of one-half of the excited molecules was 2.0 ± 0.1 and 4.6 ± 0.2 cm at 300 and 475 °K, respectively. The results from low-pressure experiments were used to deduce the collisional deactivation efficiency of CH2C1F for 1,2-C2H4F2*. The experimental data were interpreted using a four-centered HF elimination activated complex model with specific rate constants calculated according to the RRKM formulation of unimolecular reactions with full pro-vision for the thermal distribution function of the chemically activated molecules. Comparison of calculated and experimental results indicates that the critical energy for HF elimination is 62 kcal mol−1 and that on the average 11 ± 3 kcal mol−1 of energy is removed from C2H4'F2* per collision with CH2CIF. Nonequilibrium chemical activation rate constants also were calculated for 1,1-C2H4F2 and n-C3H7F, and comparison was made with the published experimental data. The temperature dependence of the chemical activation rate constants was of special interest and the question of the temperature dependence of the collisional deactivation cross section was considered. Criticism of earlier classical Kassel treatments of the chemical activation data of these fluoroalkane systems is presented. © 1969, American Chemical Society. All rights reserved.