Excitation of fast metastable hydrogen atoms to the n=3 state in passage through gases

Abstract

A technique, previously used in the authors' laboratory, in which the H(2s) metastable population of a 5-26 keV beam of hydrogen atoms is modulated by a periodic electric quench field, has been adapted to study Balmer alpha emission in the passage of such beams through thin targets of He, Ne, Ar, Kr, H₂, and N₂. Cross section-data for excitation of H(2S) to the n=3 state have been obtained for the first time. When considered in relation to the authors' previous studies of collisional destruction of H(2S) atoms, the present data indicate that a 2s-nl-1s de-excitation mode via intermediate states n>2 only accounts for part of the observed total cross sections for de-excitation. Capture into unstable states of H^- which subsequently decay by autoionisation is therefore believed to be an important collisional destruction process in the present energy range.