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

Abujarada, S, Flathmann, C and Koehler, SPK (2017) Translational and Rotational Energy Distributions of NO Photodesorbed from Au(100). Journal of Physical Chemistry C, 121 (36). pp. 19922-19929. ISSN 1932-7447

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Abstract

We report velocity and internal state distributions of nitric oxide photodesorbed from an Au(100) single crystal using 355 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 nonthermal mechanism due to excitation of an electron from the gold substrate to the adsorbed NO; this leads to a superthermal 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.