Molecular electrostatics. Part 3.—Liquid-phase electric field induced infrared absorption in tetrachloroethylene, tetrabromoethylene, diphenylacetylene and but-2-yne

Abstract

The multiple bond symmetric stretching modes of the title compounds are formally forbidden in the infrared but occur weakly in spectra of liquid phases. Their intensification in electric fields up to 5 × 10⁷ V m^–1 is reported. The intensities and band contours of the field-induced absorption bands are consistent with their being “induced dipole infrared absorption” due to the change of molecular polarisability with vibrational amplitude in these modes. This effect, which is related to Raman scattering, has previously been observed only in diatomic gases.