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 elect ron 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 fro m that of CH(A-X) in methane and ethane. On the other hand, they are q uite similar in ethylene. The rotational temperatures of CH(B) have be en estimated by two methods; one is computer simulation of the emissio n spectra, and the other is the band intensity plot on the rotational term value. All the spectra observed are best-fitted with a single rot ational temperature. The rotational temperatures of CH(B) produced fro m methane and ethylene are monotonically decreased with increasing the incident electron energy, whereas those from ethane are constant in t he region of 14-100 eV. (C) 1997 Elsevier Science B.V.