Acoustical Absorption Arising from Molecular Resonance in Solids

Abstract

Resonance phenomena resulting in anomalously high acoustic absorption can occur whenever lattice and internal molecular vibrational frequencies overlap. Significant effects are predicted at all acoustic frequencies, without restriction to the resonance region. A method is given for calculating resonance absorption using available molecular constants. As an illustrative example, the magnitude of resonance absorption has been calculated for benzene. The predicted absorption is 0.5 ${\mathrm{cm}}^{\ensuremath{-}1}$ at the 10-Mc/sec frequency, orders of magnitude larger than have been observed in other single crystals. In order to test this prediction, measurements of absorption were made on a large single crystal of benzene yielding at 10 Mc/sec, 0.25 ${\mathrm{cm}}^{\ensuremath{-}1}$. This agreement between absorption and calculated values is considered adequate, confirming the phenomenon.