Abstract

Absolute emission cross sections for production of atoms in the n = 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 n = 2 and Balmer-α, β, γ, and δ 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 n = 2 level, however, it has been possible with the aid of previous investigations to identify some transitions which may lead to both the 2s and 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.

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