SCATTERING STATE-SELECTED NO+ ON GAAS(110) - THE EFFECT OF TRANSLATIONAL AND VIBRATIONAL-ENERGY ON NO- AND O- PRODUCT FORMATION

The scattering of state-selected NO+(X(1) Sigma(+), upsilon=0-6) on GaAs(110) was explored across the hyperthermal energy region. Relative yields and velocity distributions for scattered anionic products NO-(X(3) Sigma(-), upsilon=0) and O-(P-2) were measured as a function of the number of vibrational quanta and collision energy for NO+(X(1) Sigma(+), upsilon=0-6) incident on the surface. Facile neutralization along the inbound trajectory forms vibrationally excited NO((II)-I-2) immediately prior to surface impact. Electron attachment to form NO-(X(3) Sigma(-), upsilon=0) occurs near the distance of closest approach between the molecule and surface. With regard to O-(P-2) emergence, a collision-induced dissociation mechanism is consistent with the observed 25 eV threshold. Incident vibrational energy is as much as ten times more effective than translational energy in forming O-(P-2). This paper represents the first experimental investigation into the effect of vibrational energy on electron transfer and dissociation of ions at surfaces and highlights the unique interplay between translational and vibrational motions in an ion/surface encounter.