The electron energy dependence of the Doppler profiles of the Balmer-α emission from H2, D2, CH4 and other simple hydrocarbons by electron impact

The Doppler profiles of the Balmer-α emission by electron impact have been investigated through varying the electron energy by using an etalon-grating monochromator with a high-resolving power. In the cases of H2 and D2, the spectral profiles of the Balmer-α emission consist of only one narrow component at an electron energy below 25 eV and another broad component appears above 30 eV, which indicates that there are two kinds of precursors leading to H* (3) or D* (3) responsible for the observed Balmer-α emission. The average kinetic energies of H* (3) have the same values as those of D* (3); that is, 0.2 eV and 6.7 eV for the above two components, respectively. In the case of hydrocarbons, the spectral profiles have no structure at any electron energy and the widths of the spectra increase with an increase in the electron energy. Especially for CH4, this trend is explained by comparing the above results with that on H* (high Rydberg) produced from CH4 by electron impact. (Auth.)