Potential energy surfaces for F-H2 and Cl-H2:: Long-range interactions and nonadiabatic couplings

The intermediate and long-range behavior of the three lowest doublet potential energy surfaces for the F(P-2(j))H-2 and Cl(P-2(j))-H-2 systems has been studied, using a harmonic expansion of the potential, where the dependence on the relative orientation of the half-filled orbital of the open-shell atom and the molecular axis has been given in terms of bipolar spherical harmonics, whereas the coefficients modulate the effect of the variation of the intermolecular distance. The contribution of van der Waals, electrostatic, and charge-transfer interactions to the strength and the intermolecular distance dependence of each radial term are derived from previous molecular beam scattering experiments and from correlation formulas. The latter provide the link of these quantities to basic properties of the interacting partners. Besides describing elastic and inelastic channels, these surfaces also provide accurate information on the entrance channel for reactions.