Electron capture in collisions of protons with CO molecules in the keV region: The steric effect

Electron capture resulting from collisions of H+ ions with CO molecules has been investigated based on the molecular representation within the fully quantum-mechanical formalism below 10 keV/u. Three different molecular configurations have been considered for collision dynamics, i.e., (i) the proton approaches the center of mass of the CO molecule in the perpendicular configuration, (ii) the proton approaches the C atom in the collinear configuration, and (iii) the proton approaches the O atom in the collinear configuration. Electron-capture dynamics and corresponding capture cross sections depend very sensitively on the molecular configuration, thus revealing a strong steric effect. The capture cross section from the CO electronic ground slate is about 1.3 x 10(-15) cm(2) at 10 keV/u, which is in good agreement with experimental findings. Differential cross sections (DCS's) for three molecular orientations have been examined both for elastic and electron-capture processes, and the DCS averaged over all the configurations was found to agree well with a measurement from 0.02 degrees to 1 degrees at 1.5 keV/u.