Vibrationally resolved inelastic scattering and charge transfer in H+ +C2H2 collisions

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Abstract
Differential total cross sections and time-of-flight spectra for inelastic scattering and charge transfer of protons with acetylene have been measured in a crossed molecular beam apparatus at 30 eV collision energy. Both vibrational excitation of the C–C stretch and C–H stretch vibrations are resolved in the time-of-flight spectra. The angular distributions indicate the existence of a potential well in the entrance channel of 1.2 eV. The angle dependence of the time-of-flight spectra reveal that the stiff C–H stretch vibrations are preferentially excited in grazing collisions by long range electrostatic multipole interactions, whereas the C–C stretch vibrations although softer are only excited by a short range interaction. The vibrational normal modes observed to be excited can be explained in terms of a proposed potential hypersurface and the associated nonadiabatic couplings and vibronic symmetry correlations.