| Abstract
| - The electron-stimulated luminescence (ESL) from amorphous solid water and crystalline ice films depositedon Pt(111) at 100 K is investigated as a function of the film thickness, incident electron energy (5−1000 eV),isotopic composition, and film structure. The ESL emission spectrum has a characteristic double-peaked shapethat has been attributed to a transition between a superexcited state (C̃) and the dissociative, first excited state(Ã) in water: C̃ → Ã. Comparing the electron-stimulated luminescence and O2 electron-stimulated desorption(ESD) yields versus incident electron energy, we find the ESL threshold is ∼3 eV higher than the O2 ESDthreshold, which is close to the center of the emission spectrum near 400 nm and supports the C̃ → Ã assignmentfor the ESL. For thin films, radiative and nonradiative interactions with the substrate tend to quench theluminescence. The luminescence yield increases with coverage since the interactions with the substrate becomeless important. The ESL yield from D2O is ∼4−5 times higher than that from H2O. With use of layered filmsof H2O and D2O, this sizable isotopic effect on the ESL is exploited to spatially profile the luminescenceemission within the ASW films. These experiments show that most of the luminescence is emitted fromwithin the penetration depth of the incident electron. However, the results depend on the order of the isotopesin the film and can be modeled by assuming some migration of the electronically excited states within thefilm. The ESL is very sensitive to defects and structural changes in solid water, and the emission yield issignificantly higher from amorphous films than from crystalline ice.
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