Photoinduced multi-mode quantum dynamics of pyrrole at the π1σ∗– S0S0 conical intersections
The photoinduced dynamics of pyrrole at the A12(πσ∗)– S0S0 and B11(πσ∗)– S0S0 conical intersections has been investigated by multi-mode time-dependent quantum wave-packet calculations. Diabatic potential-energy surfaces have been constructed for both conical intersection using accurate multi-reference ab initio electronic-structure calculations. In addition to the NH stretching coordinate, the three (four) symmetry-allowed coupling modes of A2A2 (B1B1) symmetry have been considered for the A12(πσ∗)– S0S0 (B1(πσ∗)– S0S0) conical intersections. Wave-packet dynamics calculations have been performed for three-dimensional models, taking account of the two dominant coupling modes of each conical intersection. The electronic population-transfer processes at the conical intersections, the branching ratio for the dissociation to the ground and excited states of the pyrrolyl radical, and their dependence on the initial preparation of the system have been investigated. It is shown that the excitation of the NH stretching mode strongly enhances the photodissociation rate, while the excitation of the strongest coupling mode has a pronounced effect on the branching ratio of the photodissociation process. Although the inclusion of the second (weaker) coupling mode has little effect on the electronic population dynamics, it leads to interesting changes of the nodal pattern of the wave packet at the conical intersections. The calculations provide insight into the effect of the multiple coupling modes on the process of direct photodissociation through a conical intersection.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 190, Issues 2–3, 15 August 2007, Pages 177–189