New insights into photodissociation dynamics of cyclobutanone from the AIMS dynamic simulation.

Abstract

In this work, the combined electronic structure calculations and non-adiabatic dynamics simulations were performed for understanding mechanistic photodissociation of cyclobutanone at ∼248 nm. Besides the stationary and intersection structures reported before, two new conical intersections between the ground (S0) and the first excited singlet (S1) states were determined in the present study, which were confirmed to be the new S1 → S0 funnels by the ab initio multiple spawning dynamic simulation, giving rise to products in the S0 state selectively. The time evolution of the S1 electronic population was fitted with the pure exponential formulae, from which the S1 lifetime was estimated to be 484.0 fs. The time constant for the S1 α-cleavage is calculated to be 176.6 fs, which is based on the present dynamics simulation. As a result of the ultrafast S1 processes, the statistical distribution of the excess energies is prevented in the S1 state. The S1 dynamic effect (the nonergodic behavior) was predicted to be an important factor that is responsible for the wavelength dependence of the branching ratio of photodissociation products, which will be discussed in detail.