Electron-stimulated desorption of D{sup +} from D{sub 2}O ice: Surface structure and electronic excitations

Journal Article · Fri Aug 01 04:00:00 EDT 1997 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.56.4925· OSTI ID:538549

Sieger, M T; Simpson, W C; Orlando, T M ^[1]

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1. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, MSIN K-14, Richland, Washington 99352 (United States)

We present a study of the electron-stimulated desorption of deuterium cations (D{sup +}) from thin (1{endash}40 ML) D{sub 2}O ice films vapor deposited on a Pt(111) substrate. Measurements of the total yield and velocity distributions as a function of temperature from 90 to 200 K show that the D{sup +} 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 (TOF) distribution is at least bimodal, indicating multiple desorption channels. A decomposition of the TOF distributions into {open_quotes}fast{close_quotes} and {open_quotes}slow{close_quotes} channels shows structure as a function of excitation energy, film thickness, and temperature. The D{sup +} 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 {approximately}160 K causes a drop in total desorption yield. The temperature dependence of D{sup {minus}} desorption via the {sup 2}B{sub 1} dissociative electron attachment resonance is very similar to the slow D{sup +} 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{sub 1} bands. {copyright} {ital 1997} {ital The American Physical Society}

• Research Organization: Pacific Northwest National Laboratory
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 538549
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 8 Vol. 56; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
CATIONS
DESORPTION
DEUTERIUM
DISSOCIATION
ELECTRON BEAMS
EXCITED STATES
HEAVY WATER
ICE
PHASE TRANSFORMATIONS
RADIATION EFFECTS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
THIN FILMS