Investigation of geometric phase effects in photodissociation dynamics at a conical intersection

Abstract

We investigate the effect of the geometric phase (GP) on photodissociation dynamics at a two-dimensional symmetry-allowed conical intersection (CI). To disentangle the pure effect of the GP from other effects due to non-adiabatic couplings between the two coupled potential energy surfaces, we perform two different calculations, one adopting the diabatic representation which implicitly includes the GP, and another one using the adiabatic picture where GP effects are excluded. To interpret the impact of the GP on nuclear dynamics, we use a recent topological approach (Althorpe et al., 2008 [45]) to completely unwind the nuclear wavefunction from around the CI. This unwinding allows us to extract from the nuclear wavepacket two contributions of reaction paths that wind in different senses around the CI. The solely effect of the GP is to change the sign of the relative phase between their corresponding wavefunctions, and hence to convert any constructive (destructive) interference of the two components, in the asymptotic dissociative limit, into a destructive (constructive) one. This results in a change of the product-state vibrational distribution from only-even (-odd) quanta progression to only-odd (-even) quanta progression. Although our calculations are based on a reduced-dimensionality model Hamiltonian, our observations and conclusions should apply to realistic polyatomic molecules, and could be useful to interpret product-state vibrational distributions of photodissociation experiments.