INTERACTION OF ELECTRONS WITH LATTICE VIBRATIONS IN AMMONIUM CHLORIDE AND AMMONIUM BROMIDE

Energy loss spectra of polycrystalline NH4Cl and NH4Br films have been studied between 10 and 400 meV using 30-keV electrons. The resolution of the spectrometer was between 4 and 10 meV, the scattering angle smaller than 1.2×10-4 radian. Strong energy losses and gains were found near 20 meV corresponding to excitation of translational lattice vibrations wellknown from reststrahl measurements. Weaker energy losses above 100 meV are due to excitation of ammonium ion fundamentals and their interaction with torsional vibrations and, presumably, with translational lattice vibrations. In this energy loss range agreement is stated concerning the general behaviour between energy loss and infra-red absorption spectra. In the finer details, however, striking deviations occur, which must be ascribed to the different interaction mechanisms of lattice vibrations with electrons and photons, respectively. © 1969 Springer-Verlag.