Mg+(S-2) and Mg+(P-2) in reaction with H-2((1)Sigma(+)(g)): A description of the energy surfaces explaining the mechanisms

The lowest two potential energy surfaces which involve Mg+(P-2) and Mg+(S-2) atoms interacting with H-2 molecules are computed to describe both the intermediate complex [MgH+2] formed during their reactive approaches and the asymptotic outcomes of MgH+ +H or of Mg+ +H-2. The calculations clearly reveal the presence of an avoided crossing between the two surfaces near the T-geometry of the complexes and the existence on the upper surface of regions where the ionic atomic states of magnesium are "coordinated" with either H-2((1)Sigma(+)(g)) or H-2 ((3)Sigma(+)(u)) states. The implications of these structural results with respect to the existing experiments in cold ion traps are discussed and shown to provide already a qualitative explanation for the final formation of MgH+/MgD+ ions in the trap. In fact, a simplified treatment of the nonadiabatic coupling effects in the region of closest approach between the two Born-Oppenheimer surfaces is given via Landau-Zener curve crossing models and are found to already yield a realistic picture of the behavior seen by the experiments. (C) 2013 Published by Elsevier B.V.