Rotational distributions and threshold energies of the CH(B-X) emission by controlled electron impact on methane, ethylene, and ethane

Excitation functions and emission spectra of CH(B-X) produced in electron impact on methane, ethylene, and ethane have been measured. There are three thresholds in the excitation functions of all the molecules. The shape of the CH(B-X) excitation function is clearly different from that of CH(A-X) in methane and ethane. On the other hand, they are quite similar in ethylene. The rotational temperatures of CH(B) have been estimated by two methods; one is computer simulation of the emission spectra, and the other is the band intensity plot on the rotational term value. All the spectra observed are best-fitted with a single rotational temperature. The rotational temperatures of CH(B) produced from methane and ethylene are monotonically decreased with increasing the incident electron energy, whereas those from ethane are constant in the region of 14-100 eV.