Production of Excited Atoms by Impact of Fast Electrons on Molecular Hydrogen and Deuterium

Absolute emission cross sections for production of atoms in the $\text{n\hspace{0.17em}=\hspace{0.17em}2–6}$ excited states have been determined for dissociative excitation of molecular hydrogen and deuterium by electrons having energies in the range from 0.05 to 6 keV. The excited atoms have been observed by optical detection of their fluorescence, Lyman‐α radiation in the case of $\text{n\hspace{0.17em}=\hspace{0.17em}2}$ and Balmer‐α, $\mathrm{\beta ,\; \gamma }$ , and $\delta$ radiation in the case of the higher states. In general there is more than one possible molecular transition which can lead to dissociation into a particular atomic state. In the case of the $\text{n\hspace{0.17em}=\hspace{0.17em}2}$ level, however, it has been possible with the aid of previous investigations to identify some transitions which may lead to both the $\text{2s}$ and $\text{2p}$ atomic states. For the formation of the higher excited states the systematics of the processes has been determined by means of analysis of the data in the Bethe–Born approximation. A strong isotope effect was found for the production of excited atoms from molecular hydrogen and deuterium. Approximately 20% fewer excited atoms are formed in the case of the heavier isotope. This difference arises due to a competition between dissociation and other processes, in particular autoionization.