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 S-2) from amorphous D2O water films has been studied using laser resonance -enhanced multiphoton ionization spectroscopy. The D (1 S-2) desorptio n product has a similar to 6.5 +/- 0.3 eV threshold energy, relative t o the vacuum level, and a low velocity distribution. ESD of electronic ally excited D (n greater than or equal to 2 S-2) was not detected usi ng photoionization schemes. A small metastable (n greater than or equa l to 2 P-2) desorption yield and/or emission of ultraviolet (UV) photo ns (hv greater than or equal to similar to 6 eV) was detected at incid ent electron energies >25 eV, using a multichannel plate detection tec hnique. We attribute the ground state D desorption to exciton decay an d associate the small metastable/UV photon emission yield with dissoci ation of doubly excited states and efficient autoionization.