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 excimer laser radiation. Detailed product state distributions are obtained using (2+1) resonance enhanced multiphoton ionization. The CO translational energy can be characterized by a temperature (T=110±{}15 K) significantly lower than that of the substrate (T=295 K). The CO rotational state distribution is non-Boltzmann and there is step structure every four or five rotational states. The evolution of CO emission as a function of laser exposure shows no incubation period or enhanced CO photodesorption over time. The CO yield is linear with laser power and displays no detectable threshold. The low kinetic energy of the desorbed CO and the nonthermal CO distributions implicate the decay of a surface species or state.