SEMICLASSICAL WAVE PACKET DYNAMICS IN NONADIABATIC PROCESSES - THE CONICAL INTERSECTION BETWEEN THE X AND A STATES OF C2H4+

Autocorrelation and probablitity functions are calculated by semiclassical wave packet dynamics for the nuclear evolution of C2H4+ in its A state, connected with the X state via a conical intersection. Three distinct choices of potential energy surfaces were made: the canonic diabatic surface H22, as defined by Köppel, the adiabatic surface E2 and the Nikitin diabatic one. The wave packet is expanded in a Gaussian basis set restricted to 40 functions. The influence of the initial Gaussian width as well as the influence of freezing this width or not is studied. Taking into account the fact that this basis set is very small, one can conclude that the results are in qualitative agreement with those obtained by Köppel. The apparent discrepancy between the canonic diabatic autocorrelation function and the exact one could be explained by the existence of a dynamical condition for the choice of the diabatic potential energy surface. In the case of C2H4+(A), the behavior during the relaxation cannot be considered as essentially diabatic or adiabatic: it is intermediate.