Far-infrared absorption spectra of water, ammonia, and chloroform calculated from instantaneous normal mode theory

Abstract

Instantaneous normal mode ͑INM͒ theory was used to calculate absolute far-infrared absorption spectra of water, ammonia, and chloroform. Three procedures for weighting the INM density of states to yield absorption intensities were tested against spectra based on dipole time correlation functions generated from molecular dynamics ͑MD͒ simulations. Weighting method I, which utilizes only the rotational character of a mode in determining its contribution to absorption, performed slightly better than method II, a more exact treatment which incorporates the extent to which a mode is IR-active. Method III, which includes the contributions of induced dipoles, was successful in describing the influence of induced dipoles on the far-infrared spectra of the model liquids. The contribution to absorption of unstable modes with imaginary frequencies was found to be significant at low frequencies, and was treated by a simple approximation. Agreement between INM theory and the MD analysis was quite good for chloroform and ammonia, but less so for water. Agreement with experimental data in the range of 4-100 cm Ϫ1 was generally poor, but no worse than that for the MD calculations, primarily reflecting the simple intermolecular potentials used rather than the computational method itself.

Dielectric relaxation of electrolyte solutions using terahertz transmission spectroscopy

“…Such measurements have been performed for polar and nonpolar solvents including water, alcohols, carbon tetrachloride, liquid benzenes, as well as various solvent mixtures. [2][3][4][5][6][7][8][9][10] In this work, we obtain corroborating results for pure water, methanol, and propylene carbonate, and extend our attention to lithium salts dissolved in them. As in previous studies, 4,11,12 we use the Debye-based dielectric relaxation model which describes the dielectric relaxation as diffusive reorientational motions in the liquid.…”

Vibrational spectroscopy of HOD in liquid D2O. II. Infrared line shapes and vibrational Stokes shift

“…The oscillation can be identified as arising from the hindered translations ͑hydrogen-bond stretching͒ of the HOD and a D 2 O molecule. 18,[43][44][45] For each transition values for ⌬ and , and their product, are given in Table III. As Fig.…”

Modeling of the behavior of water and soot contaminated oils in the terahertz range

“…water vapor) a combination of collective translational and rotational vibrations are significant for this continuous behavior. 13 A detailed analysis of dissolved water-in-oil mixtures, where the water molecules are bound in the polyglycol structure via hydrogen bonds can be found elsewhere. 14 Here, we review only the results.…”