OH-Stretch Raman Multivariate Curve Resolution Spectroscopy of HOD/H2O Mixtures

Recently, in an attempt to quantify the role of intermolecular OH stretching vibrational couplings in liquid water, experimental Raman spectra of HOD/H2O mixtures were analyzed using the multivariate curve resolution (Raman-MCR) algorithm. This algorithm allowed for the separation of the HOD solute-correlated spectrum from the spectrum of bulk water. The former spectrum highlights features arising from HOD itself as well as from perturbations it induces on the surrounding H2O molecules. In this work, we apply a mixed quantum-classical methodology developed in our group to simulate the isotropic Raman-MCR spectra of HOD/H2O mixtures. Our results illustrate that intermolecular coupling leads to broadening and a red shift of the OH stretching band, in good agreement with the experiment. Our theoretical analysis provides a molecular-level interpretation of Raman-MCR experiments on HOD/H2O mixtures, suggesting that perturbations affecting the OH stretching vibrational mode of HOD result from intermolecular vibrational coupling to surrounding H2O molecules extending well beyond the first solvation shell.