Dynamics of ionization of H2 by Ne*(3P) investigated by electron spectroscopy

The Penning ionization reaction Ne*(2p(5)3s 3P)+H2-->[NeH2]+ +e- has been studied in crossed supersonic molecular beams with electron-energy analysis at four collision energies E = 1.83, 2.50, 3.16, and 3.89 kcal/mol. The electron kinetic-energy spectra, which directly reflect the ionizing transition region, show resolved peaks assignable to v' = 0-4 of H2+. The vibrational populations deviate systematically from Franck-Condon behavior, suggesting that the discrete-continuum coupling increases with H2 bond stretching. Each peak displays both increasing breadth and increasing blueshift with increasing E, and the blueshift also increases with increasing v'. The first two properties are consistent with a predominantly repulsive excited-state potential-energy surface, while the last is speculated to be a reflection of the rHH dependence of the ionic surface. Quantum scattering calculations based on ab initio potential surfaces for the excited and ionic states in spherical and infinite-order-sudden rigid rotor approximations are in semiquantitative agreement with the measurements. Discrepancies suggest changes in the imaginary, absorptive part of the excited surface, which probably can be best effected by multiproperty fitting calculations.