Molecular charge transfer. II. Experimental and theoretical investigation of the role of incident-ion vibrational states in O2+–O2 and NO+–NO collisions

Charge‐transfer cross sections are measured for the ${\mathrm{O}}_2^{+}{\mathrm{–O}}_2$ and NO⁺–NO systems and are compared with those calculated from a theoretical multistate impact parameter model for which the resulting coupled first‐order differential equations are solved numerically. Convergence in the theoretical total cross sections is achieved by the systematic introduction of as many as 54 product states to the wavefunction expansion for the total system. At high kinetic energies (∼2 keV) the computed cross sections are controlled predominantly by the magnitude of the vibrational overlaps between the reactant and product states, and multiquantum transitions do occur with high efficiency. At lower energies, the energy defects and vibrational overlaps of the various product channels tend to control the reaction pathways. Total charge‐transfer cross sections measured as a function of reactant ion vibrational and translational energy are found to be in general accord with the computed multistate cross sections. In the low velocity limit, an approximation which assumes that all product channels with small energy defect are degenerate with the incident channel provides a reasonable description of the charge‐transfer process at ion kinetic energies less than 200 eV.