Molecular dissociation by electron impact: Optical emission from fragments of methane, ethylene, and methanol

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Abstract
We have measured relative excitation functions for the production of electronically excited fragments by electron impact dissociation of methane, ethylene and methanol from 0 to 2000 eV. At low impact energies, 10–50 eV, the measured appearance potentials are correlated to specific dissociation limits and, when possible, to specific excited states of the parent molecules. It is found that below ∼25 eV superexcited states play the dominant role in producing these fragments. Fano plots have been constructed to determine the types of molecular excitation involved. In general, most of these excited fragments are produced through optically forbidden transitions.