Rotational Energy Transfer in Molecular Collisions. I. Resonant Case

Abstract

The resonant rotational energy transfer of the type M( J =1)+M( J =0)→M( J =0)+M( J =1) has been studied theoretically. M( J ) is a linear polar molecule with the rotational quantum number J . The impact-parameter PRS (Perturbed Rotational State) and the impact-parameter CC (Close-Coupling) methods are applied. The straight-line trajectory and the pure dipole-dipole interaction are assumed. Validity of these simplifying assumptions is discussed. It is found that the energy transfer cross section becomes very large at low collision velocities and that it increases rapidly as the velocity decreases. The results are applicable to any identical linear polar molecules as long as the basic assumptions stated above are valid. For HF+HF, the theoretical prediction is compatible with the recent experimental findings by Vohralik and Miller at the collision energy 0.15 eV.