Water in toluene revisited: vibrational patterns in the stretching region

The symmetric (nu (1)) and antisymmetric (nu (3)) stretching bands of water monomers in toluene are revisited using two approaches: (i) calculation of dipole autocorrelation functions (ii) the solvatochromic behaviour of both vibration frequency shifts. The time constants extracted from the autocorr elations account for meaningful differences between the couplings establish ed by the antisymmetric and symmetric vibrations with the solvent. The dipo le autocorrelation function for the symmetric stretching band fits well a L orentzian spectral density and shows a higher contribution to hindered rota tion relatively to the one obtained from the antisymmetric stretching. The spectral shifts of stretching frequencies in toluene and in other relevant solvents were interpreted as arising from the electronic and orientational polarisations. Characteristic donor/acceptor interactions also contribute t o the red shift and were tested by using empirical solvent basicity scales such as Kamlet-Taft beta and the recently proposed SE. The deviations detec ted in toluene as regards the continuum dielectric predictions are quantita tively treated and account for the specific interaction between the water a nd the molecular pi electron system referred to in the literature. (C) 2001 Elsevier Science B.V. All rights reserved.