Motions of Molecules in Condensed Systems. II. The Infra-Red Spectra for Benzene Solid, Liquid, and Vapor in the Range from 3 to 16.7 μ

Abstract

Infra-red spectra are compared throughout the interval from 600 to 3300 wave numbers for the same amount of benzene existing separately as solid at 3°, liquid at 8°, and vapor at 20°C. The comparison demonstrates convincingly that (1) predictable selection rules for the solid are obeyed strictly, (2) there are no selection rules operating in the liquid phase, (3) the shift of molecular frequencies induced by successive stages of condensation is small and can be ignored in the approximation that regards the vibrations of an isolated molecule as harmonic ones, (4) the intensification of components of the spectrum accompanying changes of state proceeds as predicted qualitatively in an earlier paper, (5) all proposed complete assignments of the fundamental frequencies of benzene require revision. The components appearing in the several spectra are classified in accordance with a scheme suggested by the selection rules for the vapor and solid.