Critical Examination of Vibrational Energy-Transfer Theory

An accurate He–H2 interaction potential is used to test the validity of the potential that has been employed in energy transfer theory. It is found that a model based on the assumption of additive exponential potentials acting between atomic centers does not reproduce the forces, matrix elements, or transition probabilities derived from the exact potential. The cross section for vibrational excitation is critically dependent on the details of the intermolecular potential; it is particularly sensitive to small differences in the diagonal matrix elements of the interaction potential. The discrepancies that are found for the relatively simple He–H2 system raises serious concern about the general validity of the model potential, particularly in its dependence on the internal coordinate of the oscillator.