The vibrational spectrum of 1,4-dioxane in aqueous solution - theory and experiment

Continuum solvation models become unreliable when the dissolved molecule has specific interactions with the solvent. The present work focuses on comparison between a representative continuum solvation model, the conductor-like screening model (COSMO) and the explicit solvation model (ESM). Other continuum solvation models behave similarly to COSMO. Vibrational spectroscopy is a sensitive test of these models. Their performance for reproducing vibrational frequencies is examined by comparison with our experimental results on 1,4-dioxane dissolved in water. COSMO reproduces the frequency shifts only in the CH stretching vibration region but fails in the lower frequency range dominated by CC and CO stretching and deformations. It often predicts the wrong signs for the frequency shifts and the root-mean-square (RMS) deviation between the calculated and observed shifts is large (nearly 9 cm(-1)). The explicit solvation model, in which representative dioxane-water clusters are considered, provides accurate solvent frequency shifts, with the correct sign in the overwhelming majority of cases and the RMS deviation is below 2 cm(-1) in the low-frequency range. However, it performs slightly worse than COSMO for CH stretching. Surprisingly it was also found that the combined COSMO + ESM model performs worst of all three models considered in this work.