Wave packet methods for the direct calculation of energy-transfer moments in molecular collisions

We present a new wave packet based theory for the direct calculation of energy-transfer moments in molecular collision processes. This theory does not contain any explicit reference to final state information associated with the collision dynamics, thereby avoiding the need for determining vibration-rotation bound states (other than the initial state) for the molecules undergoing collision and also avoiding the calculation of state-to-state transition probabilities. The theory applies to energy-transfer moments of any order, and it generates moments for a wide range of translational energies in a single calculation. Two applications of the theory are made that demonstrate its viability; one is to collinear He + H-2 and the other to collinear He + CS2 (with two active vibrational modes in CS2). The results of these applications agree well with earlier results based on explicit calculation of transition probabilities.