INITIAL-STAGE OF SODIUM CLUSTER FORMATION IN NACL AFTER INTENSE ELECTRON PULSE IRRADIATION

Optical absorption spectra of electron-irradiated NaCl after consecutive heating steps are measured. Thermal annealing of the localized electron centers and growth of the band (peaking at 2.10 eV) due to sodium clusters are examined using computer analysis of the optical absorption spectrum. It has revealed that the sodium clusters may be nucleated from the N1 centers, and that the 2.10 eV band is initially composed of two peaks appearing around 1.70 and 2.30 eV, respectively. The oscillation mode of metal aggregates on the basis of dipole-dipole interaction suggests that these two peaks are attributed to the surface plasma oscillation of planar aggregates being formed at the initial stage.