SELECTIVE EFFICIENCY OF VIBRATIONAL EXCITATIONS IN ION-MOLECULE COLLISIONS - A COMPARISON OF BEHAVIOR FOR H-H-2 AND H--H-2()

The vibrational excitation processes which occur in molecular beam exp eriments on H-2 molecules, and using H+ or H- as projectiles, are disc ussed from the theoretical viewpoint of the microscopic quantum dynami cs and in relation to the various features of the two potential energy surfaces. The present study employs the vibrational close-coupling-ro tational infinite-order sudden (VCC-RIOS) decoupling scheme and analyz es in detail the differences of behavior of the various inelastic diff erential cross sections in the small-angle region. It is clearly found that two separate mechanisms can be invoked in the two systems to exp lain the differences in efficiency between the two excitation processe s. Such mechanisms can be related in turn to specific features of the two potential energy surfaces and to their bearing on the final dynami cal observables. Rather good agreement between calculated and observed cross sections is found for both systems. (C) 1995 American Institute of Physics.