PHONON EXCITATIONS IN LOW-ENERGY-ELECTRON RESONANT SCATTERING FROM SOLID FILMS OF N(2)

Elastic scattering and excitation of the intermolecular and intramolec ular vibrational modes by electron impact on solid films of N2 is repo rted for various incident energies (1-19 eV). The scattered electron i ntensity as a function of the incident energy for the excitation of th e vibrational modes exhibits several maxima that can be ascribed to va rious electron shape resonances found in the gas phase or to variation s 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 reson ance of N2, which has the 2PI(g) symmetry, is observed to decay into m ultiphonon excitations of about 30 meV within the incident electron en ergy range 1-3 eV. The presence of the multiphonon excitations in conj unction with the suppression of resonant elastic scattering via the 2P I(g) state of N2-, which has been initially proposed by Fano et al., i s discussed in terms of a semiclassical model developed recently by Mi lls.