Desorption of ionic species from ice/graphite by femtosecond XUV free-electron laser pulses.

Siemer B, Hoger T, Rutkowski M, Treusch R, Zacharias H

Abstract

We report results of laser desorption from water ice surfaces using XUV pulses from the free-electron laser in Hamburg (FLASH). This XUV to soft x-ray FEL provides femtosecond pulses at 20-200 eV photon energy with pulse energies up to 100 µJ. The interaction of this intense soft x-ray radiation with ice (H(2)O, D(2)O) adsorbed on highly oriented pyrolytic graphite (HOPG) yields the desorption of various ions, particularly H( + ) (D( + )), O( + ), O(2)( + ) and others. For H( + ) and O( + ) ions linear desorption yields are observed, while for O(2)( + ) a highly nonlinear desorption yield with n = (2.5 ± 0.2) is found. Kinetic energies of 1.8 eV, 559 meV and 390 meV for H( + ), O( + ), and O(2)( + ), respectively, account for only a small part of the available excess energy.