The role of molecular state and orientation in harpooning reactions:: N2O on Cs/Pt(111)

The interaction of a beam of state selected and oriented N2O molecules with 1 ML of Cs on Pt(lll) is studied by means of exoelectron emission. While the immediate emission is absent for the impact of ground-state molecules it is present when the molecules are in the first excited n(2) = 1 vibrational bending mode. The observed orientational anisotropy agrees with a theory that includes the molecular orientation. The results can be explained in a picture where N2O approaches the surface with the O end and where-after harpooning-an exoelectron is emitted.