Raman Investigation of the Ice Ic - Ice Ih Transformation

TL;DR

This study uses Raman spectroscopy to analyze the transformation of metastable cubic ice (Ice Ic) into stable hexagonal ice (Ice Ih), accurately identifying transition conditions and kinetics, including activation energy estimation.

Contribution

It provides the first detailed Raman spectroscopic analysis of the Ice Ic to Ice Ih transformation, including thermodynamic conditions and kinetic parameters.

Findings

Identified the thermodynamic conditions of the Ic-Ih transition.

Measured the vibrational spectral changes during transformation.

Estimated the activation energy for the transformation process.

Abstract

Among the many ice polymorphs, ice I, that is present in nature at ambient pressure, occurs with two different structures, i.e. the stable hexagonal (Ih) or the metastable cubic (Ic) one. An accurate analysis of cubic ice Ic was missing until the recent discovery of an easy route to obtain it in a structurally pure form. Here we report a Raman spectroscopy study of the transformation of metastable ice Ic into the stable form Ih, by applying a very slow temperature ramp to the ice Ic samples initially at 150 K. The thermal behavior of the spectroscopic features originating from the lattice and OH-stretching vibrational modes was carefully measured, identifying the thermodynamic conditions of the Ic-Ih transition and the dynamics of both structure with remarkable accuracy. Moreover, the comparison of two determinations of the transformation kinetics allowed also to provide an estimation of the activation energy for this transformation process.