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.