Full dimensional ab initio dynamics calculations of electron capture processes of the H-4(+) ion

Electron capture pdrocesses of H-4(+), that is, H-4(+) + e(-) --> H-2 + H-2 , have been studied by means of direct ab initio dynamics calculations to e lucidate the reaction mechanism. The ab initio molecular orbital calculatio ns showed that the structure of H-4(+) is flexible and its intermolecular m otion H-H-3(+) is composed of a low-frequency mode. The H-4(+) ion has a wi de Franck-Condon (FC) region for the direction of the low-frequency mode. I n dynamics calculations, we assumed that all trajectories run on the ground state of H-4 and that auto-ionization does not take place once the H-4(+) ion captures an electron. A total of 120 trajectories were run from the ini tial geometries of H-4 chosen from the FC region. Each trajectory gave two kinds of hydrogen molecules: a vibrationally excited hydrogen molecule (hot -H-2) and a vibrationally ground-state H-2 (cold-H-2) The vibrational quant um number of cold-H-2 was populated only in nu = 0, whereas that of hot-H-2 was widely distributed in nu = 4-8. About 30% of the total available energ y was partitioned into the relative translational mode between hot-H-2 and cold-H-2 The reaction mechanism of the electron capture processes of H-4(+) is discussed On the basis of the theoretical results.