CALCULATIONS OF STATIC CHARACTERISTICS OF THE IONIZATION EVENT IN LOW-ENERGY HE(2 S-3)-H-2 COLLISIONS

The H-2+ (upsilon') ( ... He) vibrational population factors and energy of Penning electrons are calculated for the ionization event He(2 3S)-H-2 (upsilon'' = 0) --> [He ... H-2+ (upsilon') ]+e- taking place at a range of the He*-H-2 distances and orientations accessible by the system during low energy collisions. The approximation employed in the calculations makes full use of that the H-H coordinate is weakly coupled to the remaining ones: The system is viewed as H-2(H-2+), Perturbed by He*(He); the H-H degree of freedom is treated quantum mechanically. The dependence of the vibrational populations and Penning electron energies on the He*-H-2 distances and orientations is found to be consistent with the experimental Penning electron spectra of the system. For small He*-H-2 distances (5.5 au less-than-or-equal-to R(He-H-2) less-than-or-equal-to 7 au), a greater degree of anisotropy of the present picture of the ionization event is predicted than one would expect on the basis of general considerations. A non-vanishing probability is obtained for the ionization event leading to a highly vibrationally excited nascent Penning ion of the structure [He ... H ... H]+. The results indicate that the present static characteristics for transitions to individual vibrational levels of the nascent Penning ion might form an input to 2D models of the dynamics of the ionization event in the He*-H-2 system which are physically more relevant than those based on the (3D) trajectory surface leaking approach.