Desorption of positive ions from ionic crystals accompanying 248 nm laser irradiation

We present a study of the energy distributions of positive ions (Na+, Li+, Ca+, and Mg+) photodesorbed from cleaved NaCl, LiF, MgO, NaNO3, and CaCO3 s urfaces during 248 nm excimer laser irradiation at fluences well below the damage thresholds. The observed ion energies are significantly higher than those predicted by already existing models that allow ion rearrangement and relaxation during the electrostatic ion repulsion by the nearby photoioniz ed sites. In contrast to what one would expect, we find that treating the i ons as fixed charges and neglecting any ion rearrangement during the emissi on of the adions describes best the experimentally observed ion energies fr om all five ionic crystals. (C) 2000 American Institute of Physics. [S0003- 6951(00)00604-5].