Production of Excited Hydrogen Atoms by Impact of Fast Electrons on Some Simple Hydrocarbons

Abstract

Absolute emission cross sections have been determined for Lyman and Balmer radiation from hydrogen atoms formed in dissociative excitation of methane, methane-d4, ethane, ethylene, and benzene by impact of electrons (0.5 → 6 keV). The excited atoms have been observed by optical detection of their fluorescence. The results are analyzed in terms of the Bethe–Born approximation. It is found that the relevant collision processes go mainly via optically forbidden transitions. An isotope effect of about 20% has been measured for the productions of excited atoms from CH4 and CD4, indicating the importance of superexcited states. The cross sections for formation of excited hydrogen atoms are almost the same for the different hydrocarbons and therefore seem to be rather insensitive to the number of H atoms in the molecule.