ULTRAVIOLET-LASER-INDUCED DESORPTION OF CO AND NO FROM PT SURFACES

Desorption of CO and NO molecules chemisorbed on Pt(001) and Pt(111) surfaces at 80 K induced by ultraviolet nanosecond-pulsed laser irradiation has been studied by a resonance-enhanced multiphoton ionization technique. Desorption is not thermally driven, but induced by electronic excitation. CO desorption from Pt(111) and NO desorption from both Pt surfaces are found to be single-photon processes, while CO desorption from Pt(001) is a three-photon process. The translational, rotational, and vibrational temperatures of desorbed NO from Pt(001) are independent of pump-laser wavelength in the energy range 3.5-6.4 eV. For NO from Pt(111), on the other hand, the internal-energy distribution is strongly dependent on pump-laser wavelength. On the basis of these results, the desorption mechanism induced by valence-electron excitation for molecules chemisorbed on metals has been discussed in connection with the unoccupied electronic structures of the adsorbate and the metal.