Luminescence from Thin Solid Films at 77°K under Low-Energy Electron Bombardment

Abstract

A spectrometer system for the study of luminescence from thin solid films induced by low-energy electron bombardment is described. This technique shows promise in the study of higher energy and optically forbidden electronic transitions in parent molecules and in providing information concerning radiolytic products. Films of benzene and toluene exhibit monomer fluorescence onsetting at an excitation energy of 4.5 eV. In the case of toluene luminescence from the benzyl radical also appears. Benzene phosphorescence is observed in a cyclohexane matrix. For cyclohexane and n-hexane films, fluorescence is observed with maxima at approximately 200 and 210 nm, respectively. At impact energies above about 15 eV other emission bands appear in the alkanes which may involve excited radicals and ions. Water exhibits bands with λmax at 280 and 380 nm. The former is attributed to fluorescence of the hydroxyl radical, and the latter can plausibly be assigned to phosphorescence from either the quartet state of the OH radical or from triplet water.