FESHBACH-TYPE ELECTRON RESONANCES IN SOLID AR, KR, AND XE FILMS - DECAY INTO MULTIPHONON EXCITATIONS

We show from high-resolution electron-scattering experiments on multilayer films of Ar, Kr, and Xe that a core-excited electron resonance, which consists of the temporary attachment of an electron to an exciton, exists in the pure solid. It is located at 11.78, 9.70, and 7.85 eV, slightly below the lowest bulk exciton energy of Ar, Kr, and Xe, respectively. This resonance, which is more specifically identified as a Feshbach-type resonance, is long lived and decays by releasing a substantial amount of energy (0.1-1.0 eV) to the lattice. Its lifetime is estimated from a semiclassical analysis of the multiphonon electron-energy-loss data to be the same for all three rare-gas solids and equal to 5.6 x 10(-14) sec.