Linear concentration dependence of vibrational width and vibrational dephasing paths in aqueous nitrate solutions

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Abstract
A theoretical model of vibrational dephasing of Raman active ions in aqueous electrolyte solutions is presented in which a probe ion is coupled to the bath by direct ion-solvent and ion-ion interactions. Expression for the vibrational width in terms of concentrations and efficiencies of the vibrational frequency modulation by ion-perturber interactions is given in the fast modulation scheme. The observed linear concentration dependence of the vibrational dephasing width of the v 1(A'1) mode of NO3 - in aqueous solutions is reasonably well explained from this model, and efficiencies of the dephasing paths through NO3 --water hydrogen bonding interaction and contact NO3 --cation pair formation interaction are estimated. Anions in the solution give only a secondary effect to nitrate vibrational dephasing because of interionic repulsive forces.