Low-Energy Electron Reflection Spectrometry for Thin Films of n -Hexane, Benzene, and Ice at 77°K

A simple low-energy electron-reflection spectrometer is described. It constants of a 10−9 torr chamber fitted with an electron gum, an ultrathin film of vacuum evaporated sample, supported on a metal block at 77°K, and a Faraday cup to measure the backscattered electron current, I. Plots of I vs the incident electron energy eV exhibit some structure, more clearly exhibited by plots of dI / dV vs V which show clearly defined peaks and appear to correspond to near-resonant energy losses. For benzene these peaks are matched by spectroscopically measured electronic energy levels, including triplets. For an ice film there is a strong peak at 4.2 eV which, supported by several other recently reported measurements using other devices, is attributed to the B13 state of H2O. For n-hexane the two lowest peaks occur at ∼ 3.9 and ∼ 4.6 eV.