A state-to-state statistical-dynamical theory for large molecule collisional energy transfer

A statistical-dynamical theory of large molecule energy transfer based on state-to-state transition probabilities is derived and a demonstration calculation is presented for cyclopropane deactivation by helium. For demonstration purposes, the SSH(T) theory is used for calculating state-to-state transition probabilities, and thus the present calculations are expected to provide only general trends. Various tests for convergence of the calculations are described. The calculations are shown to be practical even for energies where the vibrational state densities exceed 10(10) states cm(-1). The results predict that energy transfer propensities persist even at very high vibrational energies. The predicted collision step size distributions resemble the exponential model, but with strong fluctuations about the mean. The predicted average energy transferred in deactivation collisions ([Delta E](down)) depends on vibrational energy, due to the changing fraction of inelastic collisions; the shape of the distribution function remains nearly unchanged. In future calculations, the SSH(T) theory will be replaced by other theories in order to obtain more accurate predictions.