Low-energy electron-impact excitation of methane, silane, tetrafluoromethane and tetrafluorosilane

Electron-impact excitation of methane, silane, tetrafluoromethane and tetrafluorosilane has been explored in a trapped-electron spectrometer. Extensive vibrational excitation of CF₄ was observed with electrons of very low incident energies. There was some evidence of multiple vibrational excitation in SiH₄ also but the results for this molecule were not totally unambiguous. Nearthreshold vibrational excitation of SiF₄ was masked by effects attributed to a large cross-section for elastic scattering. Some optically forbidden electronic states have been located and assignments suggested. Short-lived negative-ion states (resonances) affect electronic excitation of the lowest excited Rydberg state in SiH₄, CF₄ and SiF₄ as well as negative-ion production.