Optical and vibrational studies of silver molecules and microcrystallites prepared by matrix aggregation and gas aggregation techniques

Abstract

Silver molecules Ag_n, n < 10, have been prepared by matrix aggregation techniques under various experimental conditions, i.e., metal concentration, speed of layer growth, condensation temperature and type of gas (Xe–Ne). The optical absorption spectra of these molecules show several distinct absorption bands within the range 200-550 nm, and in the corresponding laser Raman spectra several lines below 220 cm^–1 are present. The spectral features of silver molecules Ag_n, n≤ 6, could be identified by comparison with experimental data from the gas phase and/or by comparing the relative intensities of pairs of bands observed for matrices formed under different experimental conditions, allowing the remaining bands to be assigned to larger silver clusters.

Silver microcrystallites with a mean diameter 2R 10 Å could be easily prepared by a gas aggregation technique. In contrast to the results of other authors we observed a shift of the surface plasmon from 3800 Å for particles with 2R≈ 100 Å to 3600 Å for particles with 2R≈ 10 Å, i.e., a shift to higher energies. The reported increase in the halfwidth with decreasing cluster size from 0.2 to 1 eV and more could also not be found. An increase of only 0.1 eV could be measured.