Differential scattering experiments on vibrational excitation in low-energy H⁺-CO₂collisions

Vibrational excitation in H + -CO 2 collisions has been measured with the crossed-beam method in the energy range E Lab =15-50 eV and for scattering angles delta Lab =0-12 degrees which include the rainbow region. With an energy resolution of about Delta E=50 meV, excitation of the various modes of CO 2 can be clearly resolved. A pronounced selectivity is found for vibrational excitation, depending on energy and angle. For scattering angles near zero the dominant transition is 010 excitation, whereas the rainbow region at higher energies shows a strong inelasticity with dominant excitation of the asymmetric stretch mode. Small-angle scattering is interpreted by a simple model, the Born approximation with long-range electrostatic interactions.