Time of flight measurements of the vibrational excitation of CH4 by collision with 3−6 eV Li+ ions

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Abstract
Angular distributions and time of flight spectra for the scattering of Li+ ions from ground state CH4 have been measured over a range of center of mass scattering angles (7° to 19°) and energies (2.7 to 6.5 eV). The spectra reveal transitions to groups of CH4 vibrational states which could be clearly resolved. As in previous studies of CO2 and N2O, very little rotational excitation is observed. The vibrational transition probabilities show an extremely strong dependence on the scattering angle, not seen in similar experiments using simpler target molecules. Certain state to state differential cross sections as well as the average energy transfer and the second and third central moments of the energy transfer are compared for Li+ + CH4, CO2, and CO. The different behavior of the average energy trnasfer for these targets is well explained by a statistical model recently developed by two of the authors.