The spectral distribution of thermally active vibrational states in an amorphous solid

Abstract

Utilizing a novel analysis which involves the product of the Raman scattered Stokes and anti-Stokes intensities in the spectral interval 8 to 550 cm −1, the spectral distribution of thermally active vibrational states was measured for silica, amorphous B 2O 3, the amorphous polymer PMMA, and neutron irradiated silica, from room temperature down to 8 K. Qualitative lineshape analysis of the spectral distribution curves required inclusion of a decaying exponential factor, exp((−2 ω)/ ω c), where ω c is a temperature dependent fitting parameter. The exponential term is taken to describe the thermal behavior of strongly interacting vibrational modes. In addition to connecting the thermal behavior of the Bose peak modes to the broad peak observed in the heat capacity of amorphous solids, the temperature dependence of the interacting modes connects the Bose peak modes to the negative Gruneisen parameter, the nonlinear behavior observed in the thermal expansion coefficient, and the proposed frequency dependence of the phonon mean free path. The connection with the Gruneisen parameter links the exponential term with Raman coupling coefficient and therefore describes the interaction of acoustic-like excitations.