Mechanism of photo-induced desorption of molecules weakly adsorbed on a metal surface

Pui-Teng Howe; Hai-Lung Dai

doi:10.1117/12.307144

30 April 1998 Mechanism of photo-induced desorption of molecules weakly adsorbed on a metal surface

Pui-Teng Howe, Hai-Lung Dai

Proceedings Volume 3272, Laser Techniques for Surface Science III; (1998) https://doi.org/10.1117/12.307144
Event: Optoelectronics and High-Power Lasers and Applications, 1998, San Jose, CA, United States

Abstract

Using mass spectrometry flight-time measurements, photodesorption of HFCO, H₂CO, CH₂CO and CH₃Cl from Ag(111) under pulsed nanosecond laser irradiation has been investigated in the experimental photon energy range of 1.17 eV <EQ hv <EQ 4.67 eV. All these molecules are physisorbed on Ag(111). No threshold behavior has been established within this energy range. The translational energy distribution of the desorbing molecules is characterized by a Maxwell-Boltzmann temperature in the range 110 - 150 K. The low translational temperatures and low photon energy thresholds, though in striking contrast to the high average translational temperatures and threshold behavior reported for photodesorption of chemisorbed molecules from metal surfaces, can be understood in terms of the prevailing electron attachment model. However, it requires that the substrate electrons attach to the molecules with positive electron affinities. In an alternative model, electron scattering excites the high frequency, v equals 1 molecular vibrational levels, possibly through dipole interactions. In this case, desorption results from vibrational predissociation in the adsorbate- surface bond.

Citation Download Citation

Pui-Teng Howe and Hai-Lung Dai "Mechanism of photo-induced desorption of molecules weakly adsorbed on a metal surface", Proc. SPIE 3272, Laser Techniques for Surface Science III, (30 April 1998); https://doi.org/10.1117/12.307144

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