Most favorable orientation for vibrational transitions in asymmetric diatomic molecules

Dependence of the probability of vibrational transitions on molecular rotations is investigated with a four-center interaction energy. A strongly angle-dependent expression of the vibrational transition probability is obtained for asymmetric diatomic molecules. As an example, the HBr-HBr collision is chosen. For this system it is shown that the molecular vibration is most efficiently excited when the velocity of relative motion is along the colinear direction of Br-H H-Br. The colinear direction H-Br Br-H is shown to be least efficient.