Experimental and Theoretical Raman Spectroscopy of Isotopically Pure and Diluted Ice VI

Abstract

We present an experimental and theoretical Raman spectroscopic study of isotopically pure and diluted ice VI at 1 GPa at room temperature. In the experiment, we measured the OHstretch Raman spectra of polycrystalline ice VI pressurized in a diamond anvil cell. We also obtained the theoretical Raman spectra of ice VI as well as ice I h on the basis of molecular dynamics (MD) simulations and a spectroscopic map. We find that the theoretical Raman spectra are in good agreement with the experimental data, which proves the applicability and accuracy of the spectroscopic map and the MD simulations not only in the ambient condition but also at the high pressure. In particular, the theoretical calculation successfully reproduces the experimental observation of the broader bandwidth of ice VI as opposed to ice I h . Through the analysis of the MD trajectories, we attribute this bandwidth difference to the site dependence of the OH-stretch frequency that takes place specifically in ice VI. The present study demonstrates how powerful the combination of experiment and theory in vibrational spectroscopy can be for gaining a microscopic understanding of complex molecular systems.