REACTION-RATE DETERMINATIONS OF VINYL RADICAL REACTIONS WITH VINYL, METHYL, AND HYDROGEN-ATOMS

Laser photolysis-kinetic spectroscopy, end-product analysis, and detailed modeling were used to investigate three reaction systems in detail. Included were vinyl-vinyl, vinyl-methyl, and vinyl-methyl-hydrogen atoms. Product ratios, as a function of the rate constants, could be approximated by using simple expressions. This greatly simplified the precise numerical modeling of these complex systems and also permitted a realistic error analysis. Reactions and rate constants (obtained at 25-degrees-C, 100 Torr of He) in units of cm3 (molecule s)-1 are summarized as follows: CH3 + CH3 --> C2H6, (0.52 +/- 0.05) x 10(-10), C2H3 + C2H3 --> C4H6, (1.2 +/- 0.2) x 10(-10); C2H3 + C2H3 --> C2H2 + C2H4, (0.24 +/- 0.05) x 10(-10); CH3 + C2H3 --> C3H6, (1.2 +/- 0.3) x 10(-10); CH3 + C2H3 --> CH4 + C2H2, (0.34 +/- 0.07) x 10(-10); C2H3 + H --> C2H4, (2.0 +/- 0.8) x 10(-10). The cross-combination rate constant obtained for vinyl-methyl is not twice the geometric mean of the vinyl-vinyl and methyl-methyl rate constants. This observation is explained on the basis that the vinyl-vinyl rate constant is faster than predicted by simple correlation arguments. The effect of bound low-lying triplet states of the product on the vinyl combination kinetics is discussed.