Fluorescence of ice by low energy electrons

Abstract

Low energy electron‐induced fluorescence at 77 °K under conditions of improved signal‐to‐noise ratio and wavelength resolution is reported, which exhibits differences with respect to high energy radiolysis and previous published work. Three distinct visible emissions are now evident, corresponding to the ∼380 nm emission in bulk irradiated samples, and each is assigned to electron–ion recombination. An intensity increase following deuterium substitution is attributed to predissociation involving states active in the known 124 nm diffuse ultraviolet absorption bands of H₂O. Ultraviolet emission at 306 nm is assigned to the hydroxyl (?²Σ⁺→?²Π) system, and while confirmed by deuterium substitution, this observation is in disagreement with previous low energy radiolysis results which report on substantial blue shift for this spectral feature to ∼280 nm. Finally, alternative radiative schemes are proposed to attempt to reconcile conflicting published data from diverse experimental methods.