Scattering aligned NO+ on Ag(111): The effect of internuclear-axis direction on NO− and O− product formation

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Abstract
Hyperthermal energy reactions of NO+ with Ag(111) were studied as a function of collision energy and the incident diatom’s internuclear‐axis direction. Laser photoselection via (1+1’) resonance enhanced multiphoton ionization (REMPI) prepared an aligned distribution of NO+(X 1Σ+, Etrans, v=0, J) prior to the molecules impact with the surface. The emergence of scattered O− products was enhanced when NO+ approached the surface with an ‘‘end‐on’’ rather than a ‘‘side‐on’’ orientation. Moreover, the magnitude of the reaction’s alignment preference increased with decreasing collision energy. The appearance threshold for O− was approximately 20 eV. Classical trajectory calculations demonstrated that these results are consistent with a collision‐induced dissociation mechanism mediated by both vibrational and rotational excitation upon impact. Reorientation of the internuclear axis during the collision drastically affects the simulated dissociation dynamics. No alignment preference for scattered NO− emergence could be discerned from the experiments. As a complement, the angular momentum mechanics are provided to predict the internuclear‐axis distribution of ions created via two‐photon REMPI.