PHOTOCHEMISTRY OF ACETYLENE - BIMOLECULAR RATE CONSTANT FOR THE FORMATION OF BUTADIYNE AND REACTIONS OF ETHYNYL RADICALS

The vacuum-ultraviolet flash photolysis of acetylene has been investigated and the mechanisms and rate constant for butadiyne production have been measured. The major photolytic decomposition path deduced is C2H2 + hv → C2H + H. A minor channel corresponding to C2H2 → C(3P) + CH2(X̃3Σg-) (6) was also suggested. Evidence suggests that butadiyne is formed in a first-order process: C2H + C2H2 → C4H2 + H (2). The rate of (2) was determined by monitoring butadiyne concentration spectroscopically and a rate constant, k2 = 3.1 ± 0.2 × 10-11 cm3 molecule-1 s-1, determined. Addition of H2 reduces the yield of C4H2 by the reaction C2H + H2 → C2H2 + H (8) and a ratio k8/k2 = 4.9 × 10-3 was obtained. The photolysis of CF3-C2H was briefly investigated. © 1979 American Chemical Society.