The Hg–H2 system: Potential energy surfaces of the low-lying states, reactivity of the 6s6p states of Hg on H2, classical dynamic study of Hg(3P1)+H2 half collision

Potential energy surfaces for HgH2 have been calculated using a nonempirical relativistic effective core )potential incorporating configuration interaction by means of the CIPSI algorithm (configuration interaction by perturbation with multiconfigurational zeroth-order wave function selected by iterative process). Core-valence polarization and correlation energy are included via a perturbative treatment. Spin–orbit coupling is introduced through an effective Hamiltonian. These theoretical results are used to discuss the experimental ones for the Hg(3P1)+H2→HgH(X 2Σ+)+H reaction. The different behaviors of the two van der Waals complexes are explained. Dynamical studies and classical trajectories calculations confirm that the dominant pathway is a direct dissociation on the first excited surface and is responsible for a highly peaked rotational distribution of the HgH product, in agreement with experiment.