VIBRATIONALLY RESOLVED INELASTIC-SCATTERING AND CHARGE-TRANSFER IN H+ +C2H2 COLLISIONS

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.