Electron capture from a hydrogen molecule at a fixed orientation of the molecular axis

Electron capture in fast-proton–${\mathrm{H}}_2$ collisions has been reexamined in the Brinkman-Kramers approximation. The interference, first noted by T. F. Tuan and E. Gerjuoy [Phys. Rev. 117, 756 (1960)], between two capture amplitudes associated with two centers in the molecule is found to be more pronounced at fixed orientations of the molecular axis as compared to the results obtained by averaging over all orientations. This interference effect varies significantly with the orientations of the molecule. For example, in a certain angular range the number of oscillations in the differential cross sections (DCS) is maximum at ${\theta }_{\rho }$=90°, ${\phi }_{\rho }$=0°, where ${\theta }_{\rho }$ and ${\phi }_{\rho }$ are the polar and azimuthal angles, respectively, of the molecular axis with respect to the incident-beam direction. The number of oscillations of the DCS decreases (i) as impact energy decreases at a fixed value of orientation and (ii) as the orientation changes from the perpendicular position (${\theta }_{\rho }$=90°, ${\phi }_{\rho }$=0°) to other orientations for a fixed proton energy. This interference effect has not yet been observed experimentally.