Low-Energy (5−40 eV) Electron-Stimulated Desorption of Atomic Hydrogen and Metastable Emission from Amorphous Ice

Low-energy (5−40 eV) electron-stimulated desorption (ESD) of D (1 2 S) from amorphous D 2 O water films has been studied using laser resonance-enhanced multiphoton ionization spectroscopy. The D (1 2 S) desorption product has a ∼6.5 ± 0.3 eV threshold energy, relative to the vacuum level, and a low velocity distribution. ESD of electronically excited D ( n ≥ 2 2 S) was not detected using photoionization schemes. A small metastable ( n ≥ 2 2 P) desorption yield and/or emission of ultraviolet (UV) photons ( h ν ≥ ∼6 eV) was detected at incident electron energies >25 eV, using a multichannel plate detection technique. We attribute the ground state D desorption to exciton decay and associate the small metastable/UV photon emission yield with dissociation of doubly excited states and efficient autoionization.