PRODUCTION OF I-ASTERISK(P-2(1 2)) IN THE ULTRAVIOLET PHOTODISSOCIATION OF CU-BRANCHED ALKYL IODIDES/

Photodissociation dynamics of a series of alpha-branched alkyl iodides at excitation wavelengths of 222, 266, and similar to 305 nm has been investigated by measuring the quantum yield (phi) of I*(P-2(1/2)) pr oduction. I is found to be the major product at 222 nm and 266 nm fro m methyl and ethyl iodides but not from the higher alpha-branched homo logs. On the contrary, I(P-2(3/2)) is the major product at similar to 305 nm for all the iodides. Assuming that I originates from the (3)Q( 0) state over the entire A-band, production of both I and I in methyl and ethyl iodides at 222 and 266 nm is explained by invoking the curv e-crossing mechanism in the upper state. The crossing probability (P) between the (3)Q(0) and le, surfaces for these two molecules has been estimated. At similar to 305 nm, simultaneous excitation to the (3)Q(0 ) and (3)Q(1) states remains a distinct possibility. For higher branch ed (i.e., i-propyl and t-butyl) alkyl iodides, the mechanism for I pr oduction is qualitatively different from that of unbranched iodides. C oupling of alpha-carbon bending vibrational modes with the C-I bond ex citation as well as the actual time spent in the excited state surface s in i-propyl and t-butyl iodides seem to be the reasons for altering the dynamics of dissociation drastically in comparison with that of me thyl iodide. (C) 1996 American Institute of Physics.