Molecular charge transfer. III. The role of incident-ion vibrational states in H+2–H2 and D+2–D2 collisions

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Abstract
Charge transfer cross sections for the H+2–H2 and D+2–D2 systems have been computed and compared with experimental measurements in the 1 eV to 5000 eV kinetic energy range. Cross sections have been calculated using a multistate impact parameter treatment of charge transfer in which the set of first order coupled differential equations resulting from the time dependent Schrödinger equation are solved numerically. At low kinetic energies the inclusion of a comparatively small number of product states results in converged cross sections. However, as the ion kinetic energy is increased, it becomes necessary to include as many as ∼100 final vibrational states in the wavefunction expansion of the system. Both the energy defects and vibrational overlaps of the different product channels have a strong influence on reactions at low kinetic energies but as the ion energy is increased the vibrational overlaps exert a relatively more important role in controlling the product state distribution. Vibrational overlaps have been computed using accurate wavefunctions which include the effects of vibration–rotation interaction. Variation of the theoretical cross sections with both ion kinetic energy and reactant ion vibrational state are in accord with experimental measurements.