Electron-stimulated desorption of D+from D2O ice: Surface structure and electronic excitations

Abstract

We present a study of the electron-stimulated desorption of deuterium cations ͑D ϩ) from thin ͑1-40 ML͒ D 2 O ice films vapor deposited on a Pt͑111͒ substrate. Measurements of the total yield and velocity distributions as a function of temperature from 90 to 200 K show that the D ϩ yield changes with film thickness, surface temperature, and ice phase. We observe two energy thresholds for cation emission, near 25 and 40 eV, which are weakly dependent upon the ice temperature and phase. The cation time-of-flight ͑TOF͒ distribution is at least bimodal, indicating multiple desorption channels. A decomposition of the TOF distributions into ''fast'' and ''slow'' channels shows structure as a function of excitation energy, film thickness, and temperature. The D ϩ yield generally increases with temperature, rising near 120 K on amorphous ice, and near 135 K on crystalline ice. The amorphous-crystalline phase transition at ϳ160 K causes a drop in total desorption yield. The temperature dependence of D Ϫ desorption via the 2 B 1 dissociative electron attachment resonance is very similar to the slow D ϩ yield, and likely involves similar restructuring and lifetime effects. The data collectively suggest that a thermally activated reduction of surface hydrogen bonding increases the lifetime of the excited states responsible for ion desorption, and that these lifetime effects are strongest for excited states involving a 1 bands ͓S0163-1829͑97͒05931-6͔

Photodesorption of ionized water clusters from water physisorbed on rare gas solids

“…The primary electronic excitations which lead to this H + desorption have been assigned to two-hole-one-electron and/or twohole-two-electron configurations. Another ESDthreshold was observed at 40 eV [3]. Souda has examined ESD of (D 2 O) n D + [n = 1-10] from D 2 O clusters adsorbed on rare gas solids and has interpreted that the desorption of the clusters is due to Coulombic expulsion between valence holes in the water cluster [7,8] and his coworkers reported the desorption of (H 2 O) n H + [n = 1-8] from ice surface (>50 ML) [9].…”

“…A variety of studies have been made on electron-and photon-stimulated desorption (ESD/ PSD) at ice surface [1][2][3][4][5][6]. It was reported that the threshold for ESD of H + from ice surface was near 21 eV [1,2].…”

Vacuum Ultraviolet Photon-Stimulated Oxidation of Buried Ice: Graphite Grain Interfaces

“…2 2 1,3 1 (Kimmel & Orlando 1996;Sieger et al 1997;Simpson et al 1997Simpson et al , 1998 were identified as products of the 2 B 1 DEA resonance with a threshold of ∼5.5 eV and peak around 7 eV for a 10 ML amorphous ice film. These DEA channels may play important roles in radical (O and OH) production at the buried graphite-ice interface.…”

Desorption of water cluster ions from the surface of solid rare gases

“…In order to reveal the dynamics of electronic excited state of water molecules, the mechanism of desorption induced by electronic transitions (DIET) of cations [5][6][7][8][9][10][11], anions [12][13][14][15] and neutrals [16,17] from condensed or adsorbed H 2 O has been investigated by several groups.…”

“…Seiger and his coworkers [7] found desorption thresholds for electron-stimulated desorption (ESD) of D + from D 2 O ice near 22 and 40 eV. The primary electronic excitations which lead to this desorption have been assigned to several two-hole one-electron and two-hole two-electron configurations, whose states are dissociative, and the kinetic energy of the proton is likely to be generated by the Coulomb repulsion of the hole pair in a water molecule.…”