Quantum and semiclassical dynamics of the Franck-Condon wave packet on the coupled potential surfaces of the (N)over-tilde2A `/(A)over-tilde(2)A ` conical intersection

We have studied the nonadiabatic dynamics of the wave packet prepared by a Franck-Condon excitation of the ground state of the NO2 molecule. We have employed diabatic potentials refined with respect to our previous works so as to have the right behaviour at the dissociative channels. We compare the results of quantum calculations, based on a Lanczos time propagation of the wave function in a bound finite basis representation (FBR), with those of a semiclassical treatment of surface hopping type. The results are in good agreement for the first complete oscillation in the bending coordinate (i.e. up to about 60 fs), with accompanying stretching motions and nonadiabatic transitions. Later, some differences arise since the wave packet undergoes large amplitude motions and eventually reaches a partial dissociation of one N-O bond, which cannot be adequately described by a quantum-mechanical bound FBR. Nevertheless, the general features of the motion remain very similar in the two treatments. Some clear oscillations can be seen in the adiabatic population while the excited diabatic population decreases monotonically. At 200 fs, about 22% of the semiclassical trajectories have dissociated to NO + O. (C) 2000 Elsevier Science B.V. All rights reserved.