Phonon excitations in low-energy electron resonant scattering from solid films of N2.

Abstract

Elastic scattering and excitation of the intermolecular and intramolecular vibrational modes by electron impact on solid films of ${\mathrm{N}}_{2}$ is reported for various incident energies (1--19 eV). The scattered electron intensity as a function of the incident energy for the excitation of the vibrational modes exhibits several maxima that can be ascribed to various electron shape resonances found in the gas phase or to variations in the magnitude of the multiple electron scattering on phonons (i.e., intermolecular vibrational modes) which may reflect the conduction-band density of states of the solid. In contrast, the intensity of the elastic peak exhibits an energy dependence that cannot be correlated with any electron resonances. However, the lowest electron shape resonance of ${\mathrm{N}}_{2}$, which has the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathit{g}}$ symmetry, is observed to decay into multiphonon excitations of about 30 meV within the incident electron energy range 1--3 eV. The presence of the multiphonon excitations in conjunction with the suppression of resonant elastic scattering via the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathit{g}}$ state of ${\mathrm{N}}_{2}^{\mathrm{\ensuremath{-}}}$, which has been initially proposed by Fano et al., is discussed in terms of a semiclassical model developed recently by Mills.