title: Semiclassical simulations of azomethane photochemistry in the gas phase and in solution.
abstract: We present semiclassical simulations of the dynamical events which follow the n --> pi excitation of an azomethane molecule: decay to the ground state, isomerization, and dissociation. Ab initio potential energy surfaces and couplings, slightly modified according to available experimental data, are employed in conjunction with a trajectory-surface-hopping method. For an isolated molecule, we show that dissociation takes place in the ground state, because the radiationless decay is very fast. The dissociation is mainly sequential: the methyldiazenyl radical first produced fragmentates very rapidly to N(2) + CH(3)*. The results of previous experiments by Lee's and Zewail's groups, from which partially conflicting conclusions had been drawn, are reproduced and interpreted. Molecular dynamics, coupled to the surface-hopping algorithm, allows us to simulate the photochemistry in acqueous solution. Here the fragmentation is suppressed because of vibrational energy loss to the solvent: only the isomerization takes place.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Cattaneo
authors.forename: M
authors.initials: M
authors.lastname: Persico