State- and orientation-dependent N2 emission in the N2O+Cs reaction

The interaction of state-selected and oriented N2O molecules in the first excited n(2) = l bending mode with one monolayer of Cs on Pt(111) is studied by means of time-of-flight mass spectroscopy in a molecular beam experiment. State-selected and oriented N2O molecules were prepared using electrostatic hexapole and dipole fields. The emission of N-2 molecules induced by the abstraction reaction (N2O + Cs --> CsO + N-2) depends strongly on the molecular state and its orientation. Direct abstraction and backscattering of N-2 molecules is observed for N2O ground-state molecules in the n(2) = 1 first vibrationally excited bending mode. A distinct steric effect has been found for N-2 molecules emitted specularly with respect to the incoming N2O molecules. These findings are explained in a picture where direct N-2 emission is triggered by resonant N2O ionization (harpooning). The results are discussed in the context of recent exoelectron emission experiments. (C) 1998 Elsevier Science B.V. All rights reserved.