Electron-impact vibrational excitation of polyatomic gases: Exploratory calculations

We present model calculations for the inelastic cross sections of electron collisions with tetrahedral molecules XH4 (X=C, Si, Ge) when only the molecular "breathing" mode, nu (1), is being excited. The collision energy range is well above the excited thresholds and up to 12 eV, where the adiabatic approximation for the inelastic T matrix is expected to hold. The results show the efficiency of the t(2) shape resonance in enhancing the inelastic process and the appearance, in the two heavier targets, of a further a(1) resonance in the inelastic channels of both molecules. The corresponding excitation rates are also computed together with estimates of the vibrational excitation functions. (C) 2001 American Institute of Physics.