DIRECT RATE MEASUREMENTS OF THE COMBINATION AND DISPROPORTIONATION OF VINYL RADICALS

The rates of removal of vinyl radicals (C2H3) by means of combination and disproportionation reactions have been directly measured at room temperature. Vacuum-ultraviolet (vacuum-UV) flash photolysis of divinylmercury was used to generate vinyl radicals, and vacuum-UV absorption kinetic spectroscopy was used to monitor the time history of vinyl radicals through their absorption at 1647.1 Å. The absolute rate constant for vinyl radical decay was determined to be 1.0 × 10-10 cm3 molecule-1 s-1. A ratio of 4.7 for the combination/disproportionation rate constants was measured by gas chromatographic analysis of the final reaction products. Absorption coefficients for the vinyl radical absorption in the 1650-Å region were redetermined. The absolute rate constants for combination and disproportionation are then 8.2 × 10-11 and 1.8 × 10-11 cm3 molecule-1 s-1, respectively.