THE PERTURBATION OF COHERENT WAVE-PACKET DYNAMICS BY ATOM MOLECULE COLLISIONS - THE NAI+AR SYSTEM/

The results of recent femtosecond pump/probe experiments on the NaI mo lecule interacting with Ar atoms under different pressure conditions ( Knopp et al., J. Phys. Chem., in press) are interpreted using classica l and quantum mechanical calculations. It is shown how the periodic qu asibound NaI wave-packet dynamics initiated by ultrashort pulse excita tion is modified through the collision process and how the pump/probe fluorescence signal changes accordingly. Furthermore it is demonstrate d how the energy transfer in the collision processes yields internally cooled NaI molecules which are more stable with respect to electronic predissociation. (C) 1997 Elsevier Science B.V.