Effects of Hydrophobic Solute on Water Normal Modes

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.