On the use of the sudden approximation for vibrational excitation in high-energy collisions, and the sensitivity of the results to the choice of potential energy surface

We evaluate the sudden approximation for vibrational excitation in H++H2 collisions in the context of the semiclassical DECENT model for the collision dynamics. The sudden approximation fails to reproduce quantitatively the results of a full dynamical treatment at relative kinetic energies less than 500 eV. We find substantial differences between our sudden-approximation cross sections calculated using an accurate adiabatic potential energy surface and those of Collins and Cross obtained using a diatomic-in-molecules potential energy surface. (AIP)