Theoretical study of the potential energy surface and differential scattering cross sections of He-Hl complex

The intermolecular potential energy surface for He-HI complex has been first calculated by employing supermolecule method and the single and double excitation coupled-cluster with a noniterative perturbation treatment of triple excitation CCSD ( T) approach using a large basis set containing the bond function set 3s3p2d1f. The potential energy surface has two potential wells. The global minimum with a well depth of 4.473 meV has been found for the linear He-l-H configuration with R, the distance of the He atom and. the center of, mass of the HI molecule, of 0.363 nm. in addition to the global minimum, there is a second minimum corresponding to the linear He-H-I configuration with a well depth of 2.996 meV and R of 0.442 nm. Then the analytic expression of the interaction potential for the He-HI complex of the ground state has been obtained by utilizing the Barker potential-type analytic function to fit the calculated intermolecular energy data. On the basis of the above results, the differential scattering cross sections (DCS) at the energy of 100 meV for collision between He atom and HI molecule have been calculated using the quantum close-coupling method. Finally, the validity of the potential energy surface of the He-HI system has been verified by comparing it with the CCSD(T) potential energy surface of the He-HX( X = F, Cl, Br) systems and by comparing their DCS at the same collision energy.