The geometric phase effect in chemical reactions

We investigate the influence of a vector potential arising due to the presence of a conical intersection in the adiabatic potential energy surface of a quasi-Jahn-Teller (JT) model and in the adiabatic hypersurface of an A + B-2 type reactive system. Reactive and non-reactive transition probabilities, calculated by time-dependent wave packet approach for a quasi-JT model, demonstrate the effect of a topological phase. The geometric phase (GP) effect has been introduced either by including a vector potential in the system Hamiltonian or by incorporating a phase factor in the adiabatic nuclear wave function. Even when we replace the operators in the Hamiltonian (with or without introducing a vector potential) with their classical variables and calculate integral and differential cross sections, we clearly observe the signature of the GP effect. Results obtained by semi-classical calculation on the same system also confirm this effect. In this context, we present also recent results obtained by quasi-classical trajectory calculations for the H + D-2 reaction. (C) 2000 Elsevier Science B.V. All rights reserved.