On the isotropic Raman spectra of isotopic binary mixtures

Abstract

A theory is developed for the isotropic Raman spectrum of nondegenerate modes in polyatomic binary mixtures. Particular emphasis is attached to isotopic binary mixtures and the problem of dipolar resonant transfer. The thermodynamic state dependences of spectral features are investigated in some detail. Attention is focused on quantities which are experimentally accessible by isotopic dilution experiments, in particular the frequency shift of the spectrum consequent upon isotopic dilution, and also the resultant changes in spectral second moments. The theory is compared with some existing experiments on specific systems, and a number of predictions are made which are capable of being tested experimentally.

Concentration dependence of the band profile parameters for the ν3(12C=O) Raman band of acetone in acetone–CCl4 binary mixtures: Experimental and Monte Carlo simulation results and their interpretation

“…Moreover, chemical and isotopic dilution gradually turn off the vibrational resonance energy transfer, usually leading to a reduction of the decay rate of the vibrational correlation function and resulting in band narrowing, although the sign of cross terms in the intermolecular potential may invert this tendency. 17,30,31 We remark that these processes also affect the position of the band, therefore different microenvironments cause the band position ͑first moment M͒ to shift with dilution, while the fluctuation of the microenvironments cause an additional band broadening leading to a nonmonotonic concentration dependence of the bandwidth.…”

“…The reason for this is described in Ref. 17. Closer to experimental verification are those elaborated for band broadening arising from process II.…”

“…One of these is given by Bratos and Tarjus 11,12,[14][15][16] and taken over by Logan,17 describing Raman band profiles of binary mixtures of van der Waals liquids. They calculated vibration and rotation time correlation functions that give rise to the line shape, making specific assumptions on the interaction Hamiltonian and using the cumulant expansion technique.…”

Non-coincidence effect in methyl ethyl ketone: a solvent-dependent Raman study

“…2). It has been shown by Logan 17 that the presence of NCE and its general vanishing on isotopic dilution indicate the presence of a resonant coupling due to transition dipole-transition dipole interactions.…”

Novel Approaches in Spectroscopy of Interparticle Inter-Actions. Vibrational Line Profiles and Anomalous Non-Coincidence Effects

“…In such case all non-resonant interactions in the solution remain the same as compared to the pure liquid, whereas resonant interactions are vanishing since the distance between molecules of the solute increases due to dilution. Isotopic dilution is therefore one of the most popular tools for studying non-coincidences [77,78].…”