State-Selected Molecular Ion/surface Scattering: Charge Transfer and Dissociation.

To address the charge transfer and dissociation processes operative in molecular ion/surface collisions, a series of state-selected ion/surface experiments are herein reported. Specifically, NO^{+ }(X ^1Sigma^{+ }) is systematically prepared in vibrational quantum states nu = 0 through nu = 6 via 2 + 1 resonance enhanced multiphoton ionization (REMPI) and scattered on single-crystal GaAs(110) through a 5-80 eV range of collision energies. These experiments characterize the NO^{+}(X ^1 Sigma^{+}) translational and vibrational energy dependencies for the two-electron transfer products NO-(X ^3Sigma^ {-}, nu = 0) and O- {(^2P)} which result from scattering NO^{+}(X^1Sigma^+ , nu = 0) on GaAs(110). Most notably, the relative O-(^2P) yield is strongly dependent upon the incident NO^ {+}(X ^1Sigma^{+}) vibrational quantum state whereas no such dependence is noted for NO-(X ^3Sigma^ {-}, mu = 0) production; furthermore, vibrational energy is roughly ten times more effective than translational energy in producing scattered O-( ^2P) ions. The results are interpreted within the context of supporting models which are utilized to describe the electron transfer and nuclear dynamics associated with a molecular ion/surface collision. Most notably, there is qualitative agreement between the classical trajectory calculations and the experimental results: accordingly, the essential energy transfer and dissociation features can be explained by a classical, collision-induced dissociation mechanism. This study represents the first investigation into the effect of vibrational energy on electron transfer and dissociation of molecular ions at surfaces and highlights the unique interplay between translational and vibrational motions in a molecular ion/surface encounter.