Collisional deactivation probabilities for chemically activated 1,1,1-trifluoroethane

✍ Scribed by P. J. Marcoux; E. E. Siefert; D. W. Setser

• Publisher: John Wiley and Sons
• Year: 1975
• Tongue: English
• Weight: 245 KB
• Volume: 7
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550070314

✦ Synopsis

We wish to communicate results from studies of the vibrational deactivation of chemically activated molecules [ 11. The present measurements are for CHaCFZ with a wide variety of bath gases which include inefficient rare gases as well as polyatomic gases ranging up to the efficiency of those investigated by Chang, Craig, and Setser [2]. The results consist of comparisons of data at high pressure, which give a measure of relative collisional deactivation efficiencies, and of extensive low-pressure data, which permit approximate assignment of a collisional transition probability model and the average energy ( A E ) lost per collision according to that model. For several bath gases experiments were done at 300°K and 195°K. The important general conclusions are (a) there is a wide spread in collisional efficiencies for various bath gases, and (b) CH 3CF 3 is particularly difficult to deactivate relative to 1,2-dichloroethane [3] and cyclopropane [4].

The photolysis [5] of CF3N2CH3 generates CH3 and CF3 radicals from which chemically activated CHBCF3" molecules are formed, with an average energy of 102 kcal/rnole [Z]. The critical energy for H F elimination producing CHz=CF2 is -68 kcal/mole [6]. Chemically activated CH3CF3* may either undergo unimolecular reaction or collisional stabilization. The nonequilibrium rate constant for this process is defined by k, = wD/S, where D is the number of molecules decomposing per unit time, S is the number of molecules stabilized per unit time, and w is the collision frequency. The proportionality between w and pressure