N–H photodissociation dynamics of electronically excited aniline: a three dimensional time-dependent quantum wavepacket study

Abstract

We have simulated the dynamics of ¹πσ* state-mediated nonadiabatic N–H bond dissociation in photo-excited aniline (C₆H₅NH₂). A three electronic state diabatic model potential, involving the ground, ¹ππ*, and ¹πσ* diabatic states, and focussing on the NH₂ degrees of freedom alone is constructed using XMS-CASPT2 energies. Using a kinetic energy operator in the polyspherical framework, wavepacket dynamics in three vibrational modes, viz. NH stretch, NH₂ out-of-plane wag and torsion, is carried out using the Chebyshev propagation scheme. For optically bright ¹ππ* excitation, the wavepacket can access the ¹πσ*/¹ππ* and ¹ππ/¹πσ* conical intersections that lie en route to dissociation. For both intersections, NH₂ out-of-plane wag and torsional motions are the most dominant coupling coordinates. Carrying out dynamics with initial wavepackets varying in excitation in the three degrees of freedom, we probe their roles in the evolution of the state populations, probability densities, and product branching for the NH dissociation process.