Vibrational dephasing of the croconate dianion in different environments

Abstract

Raman band-shape analysis of croconate dianion, C₅O₅²⁻, was performed in order to reveal the short-time dynamics of this species in different environments: aqueous solution, acetonitrile solution, and the low-temperature molten salt tetra(n-butyl)ammonium croconate, [(n-C₄H₉)₄N]₂C₅O₅·4H₂O, TBCR. Two totally symmetric normal modes were investigated, the CO stretching, ν₁, and the ring breathing, ν₂. Vibrational dephasing parameters for ν₁ and ν₂ display very different behaviour on changing the environment in which the C₅O₅²⁻ moiety is located. A quantitative explanation of the changes in parameters is not yet available, but it is argued that strong hydrogen bond with water molecules is the origin of the very different dephasing dynamics of C₅O₅²⁻ in aqueous solution in comparison with acetonitrile solution and TBCR. Thus, experimental vibrational time correlation functions nicely illustrate distinct sensitivity of different intramolecular oscillators of the solute to intermolecular dynamics, that is, distinct coupling between intra- and intermolecular degrees of freedom. Copyright © 2005 John Wiley & Sons, Ltd.