Rotational energy transfer in HF: A computational study

Close-coupled scattering calculations have been carried out for rotationally inelastic collisions between HF molecules. Integral cross sections were determined for vibrationally elastic transitions j1 j2→j ′1 j 2(v1v2), which refer to collisions HFa (v1, j1)+HFb (v2, j2)+ΔE→HFa (v1, j ′1 )+HFb (v2, j 2), where ΔE is the energy gap. Total energies between 241.1 and 3900 cm−1 (0.03 and 0.48 eV) were considered. When v1=v2, the rotational exchange transitions j1 j2→j2 j1(v1v2) are energetically resonant (i.e., ΔE=0), and the corresponding cross sections increase as the collision energy decreases. Particularly large cross sections are obtained for the j j+1→j+1 j(vv) transitions, which are both resonant and coupled to first order by the dipole–dipole interaction. When v1≠v2, the j j+1→j+1 j(v1v2) transitions are no longer resonant, and the corresponding cross sections are greatly reduced at small to moderate collision energies. The dependence of the j1 j2→j ′1 j 2(v1v2) cross sections upon the vibrational states of the molecules, the collision energy, and the interaction potential used is discussed.