CO AND CO+ PHOTODESORPTION FROM PT(001) AT 193-NM

ArF excimer laser irradiation of CO adsorbed on Pt(001) at 80 K provoked photodesorption of both CO and CO+. The neutral species was state-selectively detected and found to be rotationally cold (almost-equal-to 150 K) and vibrationally excited (almost-equal-to 800 K). The photodesorption yields of both species, CO and CO+, exhibit a F(approximately 3) and F(approximately 1.8) dependence versus fluence (F), respectively. We propose that neutral-species desorption proceeds via three-photon ionization of the adsorbate followed by reneutralization without recapture, while CO+ desorption results from a two-photon electronic excitation of the admolecule followed by its ionization due to the transfer of an electron to the metal and desorption before neutralization.