Theoretical study on the photostimulated desorption of CO from a Pt surface

H. Nakatsuji, H. Morita, H. Nakai, Y. Murata, K. Fukutani

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32 Citations (Scopus)

Abstract

Photostimulated desorptions (PSD's) of CO, CO+, and CO- from a Pt surface are studied theoretically using Pt2-CO model cluster including image force correction. Calculations are performed by the single excitation configuration interaction and the symmetry adapted cluster (SAC)/SAC-CI methods. The PSD's of the ground state CO occur as the Menzel-Gomer-Redhead (MGR) process and those of CO+ (n cation) and excited (n→π*) CO* through the modified MGR process in which the upper repulsive potential curves are nonadiabatic; the process proceeds through a sequence of nonadiabatic transitions between the similar pertinent states embedded in the metal excited bands. The excited states as the desorption channels are characterized by the excitations from the Pt-CO bonding orbitals to the antibonding MO's: metal-adsorbate chemical bond cleavage by photons which leads to a repulsive potential is essential for the PSD. The electrostatic image force interaction plays only a minor role and the present result does not support the Antoniewicz model. The calculated excitation-energy thresholds for the CO, CO+, and CO* desorptions are 1.6∼2.6, 11.3, and 11.3-12.7 eV, respectively, which explains the energy thresholds and the fluence dependencies of the incident laser in the PSD experiments. On the other hand, the PSD giving CO- would occur with the energy range of 6.2-8.2 eV, one to two photon energy of the 193 nm (6.4 eV) laser. Since the upper nonadiabatic potential curves have shallow minima, in this case, the lifetime of the CO- species would be larger than those of the CO+ and CO* species. The present study clarifies the electronic structures of the desorbed CO+, CO-, and CO* species, which have not been identified experimentally.

Original languageEnglish
Pages (from-to)714-726
Number of pages13
JournalJournal of Chemical Physics
Volume104
Issue number2
DOIs
Publication statusPublished - 1996 Jan 1
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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