PHOTOSTIMULATED DESORPTION OF CO FROM GEOLOGIC CALCITE FOLLOWING 193-NM IRRADIATION

We report the results of a photostimulated desorption study of neutral CO product from geologic calcite using very low fluence 193-nm excime r laser radiation. Detailed product state distributions are obtained u sing (2+1) resonance enhanced multiphoton ionization. The CO translati onal energy can be characterized by a temperature (T= 110+/-15 K) sign ificantly lower than that of the substrate (T= 295 K). The CO rotation al state distribution is non-Boltzmann and there is step structure eve ry four or five rotational states. The evolution of CO emission as a f unction of laser exposure shows no incubation period or enhanced CO ph otodesorption over time. The CO yield is linear with laser power and d isplays no detectable threshold. The low kinetic energy of the desorbe d CO and the nonthermal CO distributions implicate the decay of a surf ace species or state.