Angular Distribution of Metastable Hydrogen Formed by Dissociation ofH2+

Abstract

A study has been made of ${\mathrm{H}}_{2}^{+}$ dissociation by impact on targets of He, Ar, ${\mathrm{H}}_{2}$, and ${\mathrm{N}}_{2}$. Cross sections were measured for the angular distributions of metastable hydrogen, protons, and neutral hydrogen atoms resulting from dissociation. Projectile energies are in the range 4-12 keV; the angular range of the measurements extended from 0.5\ifmmode^\circ\else\textdegree\fi{} to 5.0\ifmmode^\circ\else\textdegree\fi{}. The angular distributions of metastables are consistent with their formation through excitation of the ${\mathrm{H}}_{2}^{+}$ projectile into the $2s{\ensuremath{\sigma}}_{g}$ and $3p{\ensuremath{\sigma}}_{u}$ repulsive states of ${\mathrm{H}}_{2}^{+}$. In all cases the dissociation cross section appears to be strongly peaked towards small angles between the internuclear axis of the molecule and the direction of the ${\mathrm{H}}_{2}^{+}$ projectile; in the case of $\mathrm{H}(2s)$ formed by dissociation on He, the cross section appears to vary as approximately the square of the cosine of that angle. Angular distributions vary quite markedly from one target to another.