Destruction of fast H(2s) atoms by collisions with He, Ar, H2, and N2

Abstract

Absolute cross sections for the destruction of hydrogen metastable atoms [$\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$] have been measured for impact on He, Ar, ${\mathrm{H}}_2$, and ${\mathrm{N}}_2$ in the energy range from 20 to 120 keV. Cross sections have also been measured for the collisional ionization of $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ by impact on ${\mathrm{H}}_2$ in this same energy range. The analysis of the collisional destruction of $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ includes electron capture into unbound states of the negative ion with subsequent loss of the excited state as one of the quenching mechanisms in this energy range. Collisional ionization (direct electron loss) of the metastable projectile accounts for most of the remaining destruction. Within experimental error, collisional ionization and electron capture can entirely account for the destruction by impact on He. Additional quenching mechanisms are required for impact on the other targets. It is found that about 70% of the noncapture destruction is accounted for by collisional ionization in these cases. The results for destruction by impact on the molecular gases, ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$, appear to be adequately explained by the inclusion of dipole-quadrupole electric-field quenching as the third mechanism.