Elastic and inelastic processes in ${\mathrm{H}}^{+}$+${\mathrm{C}}_2$${\mathrm{H}}_2$ collisions below the 1.5-keV regime

Electron capture and direct elastic scattering in collisions of ${\mathrm{H}}^{+}$ ions with ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ molecules are studied by using a molecular representation within a fully quantum-mechanical approach below 1.5 keV. Calculations are carried out at two different molecular configurations: (i) ${\mathit{C}}_{00\mathit{v}}$ symmetry, in which ${\mathrm{H}}^{+}$ approaches the H atom along a C—H bond in the acetylene (${\mathrm{C}}_2$ ${\mathrm{H}}_2$), and (ii) ${\mathit{C}}_{2\mathit{v}}$ symmetry, in which ${\mathrm{H}}^{+}$ approaches perpendicularly toward the midpoint between two carbon atoms. We find that electron capture in the ${\mathit{C}}_{00\mathit{v}}$ symmetry configuration takes place preferentially over that in the ${\mathit{C}}_{2\mathit{v}}$ symmetry configuration at scattering angles above 15°. The results for the ${\mathit{C}}_{2\mathit{v}}$ and ${\mathit{C}}_{00\mathit{v}}$ symmetries are comparable in magnitude below 10°, although the ${\mathit{C}}_{2\mathit{v}}$ symmetry dominates slightly at still smaller angles. Hence, interferences arising from these molecular configurations in differential cross sections for electron capture and elastic scattering processes are strongly present at angles smaller than a few degrees. Accordingly, the total cross section for the ${\mathit{C}}_{2\mathit{v}}$ symmetry is larger by a factor of 3 at 1 keV, and the difference widens as the energy decreases to the eV regime. This is because in ${\mathit{C}}_{2\mathit{v}}$ symmetry, ${\mathrm{H}}^{+}$ can have a larger overlap with the charge distribution of the ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ molecule, thus causing a stronger interaction. © 1996 The American Physical Society.