Effects of hydrophobic solute on water normal modes

• Published in: Chemical physics 2021-10, Vol.550, p.111303, Article 111303
• Main Authors: Reddy, Kambham Devendra, Joy, Albin, Biswas, Rajib
• Format: Article
• Language: English
• Subjects: Density of states; Hydrophobicity; Normal mode; Theoretical spectroscopy
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2021.111303

•Effects of hydrophobic substances on the normal modes of water.•Symmetry based decomposition of normal modes and estimation of mode mixing.•Estimation of the extent of delocalization of the normal modes of methane and water in the aqueous methane system. In this work, we examine the effects of methane, on the normal modes of water. We find methane has a weaker influence on water normal modes. We estimate the vibrational density of states and the infrared spectral density. We decompose these modes based on different vibrational characters. We observe a general decrease in intensity throughout the water stretch region in the methane-water system compared to the bulk water data. This lower intensity reflects the reduction of the number of average water molecules in the methane-water system. The stretch-bend decomposition reflects a pronounced coupling between the methane asymmetric stretch mode and the water symmetric stretch mode. We examine the methane-water data in terms of the symmetry of the central water molecule’s vibrations and find that asymmetric modes do not contribute. We also find that the vibrational modes having non-zero contributions from methane molecule are extremely localized in nature.