Theoretical study of ground and excited state potential energy surfaces for the Ca+-H2 complex

The potential energy surfaces of the Ca+-H-2 complex are calculated using the internally contracted multireference CI method (ICMR CI) and complete active space SCF (CAS SCF) reference wave functions. The calculations involve both the ground and the excited states correlating to (3d)D-2 and (4p)P-2 Ca+ terms and are carried out for C-infinity v and C-2v configurations. Anisotropy of the potential surfaces has also been analysed by computing the interaction energy for some representative points as a function of the angle between the Hz molecular axis and the Ca+-centre of mass of H-2 bond axis. The calculations have revealed the existence of a conical intersection of the lowest excited (3d)B-2(2) potential surface with the ground state one. The obtained global energy minimum of the (3d)B-2(2) potential surface lying 0.683 eV below the asymptote indicates a possible stabilization of the Ca+-H-2 complex towards formation of an exciplex in the (3d)Ca+-H-2(v = 0) collision process. The dependence of the vibrational energy levels of H-2 on the distance from Ca+ in the C-2v configuration has also been studied.