Formation of Fast Excited H Atoms Induced by Impact of H+, H2+, and H3+ Atoms on Molecular and Noble-Gas Targets

Abstract

An experimental investigation has been made of the formation of excited hydrogen atoms by charge-transfer neutralization of ${\mathrm{H}}^{+}$ and collisional dissociation of ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$. Data are presented for the formation of $\mathrm{H}\mathrm{}\left(3s\right)\mathrm{}$ induced by ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ impact on the noble gases; for ${\mathrm{H}}_2^{+}$ impact on ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, ${\mathrm{N}}_2$, and Ar, the measurements include formation of $\mathrm{H}\mathrm{}\left(3s\right)\mathrm{}$ and $\mathrm{H}\mathrm{}\left(3d\right)\mathrm{}$ states. Projectile energies range from 100 to 600 keV. The cross sections for producing hydrogen in the $n=3\mathrm{}$ states have been determined by quantitative measurement of collisionally induced Balmer-$\alpha$ emission. The contributions from the $3s$, $3p$, and $3d$ states were separated by a method employing the different lifetimes of each state. Data are consistent with previous measurements made at lower energies. In dissociation the cross sections are generally the same for the formation of the $3s$ and $3d$ states; they show a slow decrease as a function of projectile energy. Cross sections for formation of $\mathrm{H}\mathrm{}\left(3s\right)\mathrm{}$ by charge transfer show the expected rapid decrease with increasing energy. Differences between cross sections for various target gases suggest that the internal structure of the target atom will be an important factor in any prediction of these cross sections.