Translational and Rotational Energy Distributions of NO Photodesorbed from Au(100)

Abstract

We report velocity and internal state distributions of nitric oxide photodesorbed from an Au(100) single crystal using 355 nm and 266 nm photons. The velocity distributions were measured in all three dimensions independently using our novel 3D-velocity map imaging setup. Combined with the internal energy distributions, we reveal two distinct desorption mechanisms for the photodesorption of NO from gold dependent on the photon wavelength. The 355 nm desorption is dominated by a non-thermal mechanism due to excitation of an electron from the gold substrate to the adsorbed NO; this leads to a super-thermal and noticeably narrow velocity distribution, and a rotational state distribution that positively correlates with the velocity distribution and can be described by a rotational temperature appreciably above the surface temperature. Desorption with 266 nm photons leads to a slower average speed and wider angular distribution, and rotational temperatures not too far off the surface temperature. We conclude that in the absence of occupied orbitals in the substrate and unoccupied orbitals on the adsorbed NO separated by 4.7 eV, corresponding to 266 nm, the shorter wavelength desorption is dominated by a thermally-activated mechanism.

Adsorption site, orientation and alignment of NO adsorbed on Au(100) using 3D-velocity map imaging, X-ray photoelectron spectroscopy and density functional theory

“…A laser-desorbed N-O molecule which adsorbs with its molecular axis along the surface normal would on the other hand be rotationally cold, as in our case here. 31…”

“…This shows that NO has desorbed from the surface at this temperature in agreement with our previous 3D-VMI results. 31…”

Study on Mechanisms of Photon-Induced Material Removal on Silicon at Atomic and Close-to-Atomic Scale

“…Photon-induced desorption refers to the reactions in which atoms/molecules are desorbed as neutrals or ions due to electronic excitation stimulated by photons. Several models have been proposed to describe the mechanisms of photon-induced desorption; these models include the Knotek–Feibelman (KF) [ 37 , 38 ], Menzel–Gomer–Redhead (MGR) [ 39 , 40 ], and Antoniewicz model [ 41 , 42 ]. The KF model is based on the ionization of a core level, followed by an Auger decay.…”

Velocity-Selected Rotational State Distributions of Nitric Oxide Scattered off Graphene Revealed by Surface-Velocity Map Imaging

“…We hence set out to record rotational state distributions of nitric oxide radicals after collisions with graphene in our surface-velocity map imaging (VMI) setup. , VMI (typically applied to gas-phase dynamics) has recently been applied more and more to study surface dynamics, − allowing one to derive speed and angular distributions of the scattered products. A resonance-enhanced multiphoton ionization (REMPI) scheme is frequently applied in VMI studies, guaranteeing state-selectivity.…”