Collisional dissociation of H2+ and H3+ on molecular targets leading to formation of excited hydrogen atoms

Abstract

Experimental measurements have been made of the cross sections for dissociation of fast (100–700 keV) H2+ and H3+ ions to give fast H atoms in the 3s excited state; targets for this work were O2, CO, CO2, CH4, C2H6, and C3H8. The technique involved quantitative measurement of Balmer-alpha radiation emitted from fast moving fragments of the dissociated projectile. Contributions to the Balmer-alpha emission from the 3p and 3d levels were eliminated by a method that utilizes the different lifetimes of the 3s, 3p, and 3d states. It is observed that cross sections for H(3s) formation by dissociation on the hydrocarbons all exhibit essentially the same variation with impact energy and increase in magnitude with the complexity of the target; similar behavior is exhibited by the O2, CO, and CO2 group of targets. Comparison of the various cross sections suggests that one cannot assign an effective cross-section value to the constituent atoms of the target molecule.