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 $\mathrm{dI\hspace{0.17em}/\hspace{0.17em}dV}\mathrm{vs}V$ 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 ${}^3{B}_1$ state of H₂O. For n‐hexane the two lowest peaks occur at ∼ 3.9 and ∼ 4.6 eV.