ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Low intensity ir radiation at 2–15 μm desorbs HD from 1.5–4.2 K lithium fluoride (LiF) via four distinct channels. The channel most studied here involves coverages of one monolayer or less and 9–15 μm radiation, causing HD to desorb with a translational energy TB of 21 K. This process, which is attributed to a single phonon ejecting HD from its lowest bound state, is precisely linear in the radiation intensity, and its efficiency increases with increasing wavelength, reaching a maximum of ≈4×10−5 molecules per photon at 15 μm. At multilayer coverages and a surface temperature of 4.2 K, at which HD has a significant vapor pressure, we observe a photoinduced thermal desorption signal (TB=4.0–4.8 K), arising from a very small (≈0.005 K) perturbation of the crystal temperature. The evidence for thermal desorption of this channel strongly contrasts with the other three channels, which are nonthermal. A third channel involves radiation between 2.71 and 4.4 μm, which causes a very weak signal with TB≈20 K. While this region was chosen to include the HD vibrational transition at 2.75 μm, we present calculations which indicate that vibrational predesorption is not operative here. A fourth channel (TB≈34 K) is observed only for LiF containing bulk OH− impurities absorbing at 2.78 μm, and is attributed to phonons generated by the OH− excitation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.464615
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