title: Adiabatic and nonadiabatic bond cleavages in Norrish type I reaction.
abstract: One of the fundamental photoreactions for ketones is Norrish type I reaction, which has been extensively studied both experimentally and theoretically. Its α bond-cleavage mechanisms are usually explained in an adiabatic picture based on the involved excited-state potential energy surfaces, but scarcely investigated in terms of a nonadiabatic picture. In this work, the S(1) α bond-cleavage reactions of CH(3)OC(O)Cl have been investigated by using the CASSCF and MRCI-SD calculations, and the ab initio based time-dependent quantum wavepacket simulation. The numerical results indicate that the photoinduced dissociation dynamics of CH(3)OC(O)Cl could exhibit strong nonadiabatic bond-fission characteristics for the S(1) α C-Cl bond cleavage, while the dynamics of the S(1) α C-O bond cleavage is mainly of adiabatic characteristics. This nonadiabatic mechanism for Norrish type I reaction of CH(3)OC(O)Cl is uncovered for the first time. The quantum wavepacket dynamics, based on the reduced-dimensional coupled potential energy surfaces, to some extent illustrates the significance of the nonadiabatic effect in the transition-state region on the dynamics of Norrish type I reaction.
authors.affiliation: Chemistry College, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Ganglong
authors.initials: G
authors.lastname: Cui
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Sun
authors.forename: Weihai
authors.initials: W
authors.lastname: Fang