Primary products and secondary reactions in the photodecomposition of methyl halides
Abstract
CH3I, CH3Br, and CH3CI have been photolyzed at 184.9 nm and CH3I at 253.7 nm, using CO, C2H4, C2H6, C3H8, C3D8, and CD4 as scavengers to assist in the identification of the primary decomposition products. The quantum yield of methylene formation (CH3X + hv --> CH2 + HX) is less than ~10^-3 in all cases. Carbon-hydrogen bond rupture occurs with a quantum yield of in the photolysis of CH3I at 184.9 nm. Evidence is given on the relative effectiveness of CH3I and hydrocarbons in thermalizing hot CH3 radicals and on preferential abstraction from C-H bonds relative to C-D bonds by hot CH3 radicals. Rupture of the carbon-halogen bond in CH3Cl is the predominant path of photodecomposition, as earlier investigations (and the present work) show it to be in CH3Br and CH3I. The quantum yield of photosensitized CH2 production by reaction of C3H8 with I2 excited at 184.9 nm is shown to be <10^-3.