Molecular-Level Interpretation of Vibrational Spectra of Ordered Ice Phases

Abstract

We build on results from our previous investigation into ice Ih using a combination of classical many-body molecular dynamics (MB-MD) and normal mode (NM) calculations to obtain molecular level information on the spectroscopic signatures in the OH stretching region for all seven of the known ordered crystalline ice phases. The classical MB-MD spectra are shown to capture the important spectral features by comparing with experimental Raman spectra. This motivates the use of the classical simulations in understanding the spectral features of the various ordered ice phases in molecular terms. This is achieved through NM analysis to first demonstrate that the MB-MD spectra can be well recovered through the transition dipole moments and polarizability tensors calculated from each NM. From the normal mode calculations, measures of the amount of symmetric and antisymmetric stretching are calculated for each ice, as well as an approximation of how localized each mode is. These metrics aid in viewing the ice phases on a continuous spectrum determined by their density. As in ice Ih, it is found that most of the other ordered ice phases have highly delocalized modes and their spectral features cannot, in general, be described in terms of molecular normal modes. The lone exception is ice VIII, the densest crystalline ice phase. Despite being found only at high pressure, the symmetry index shows a clear separation of symmetric and antisymmetric stretching modes giving rise to two distinct features. File list (2) download file view on ChemRxiv ordered_ice_phases.pdf (4.92 MiB) download file view on ChemRxiv supp_info.pdf (315.48 KiB)

Computational Analysis of Exotic Molecular and Atomic Vibrations in Ice XV

“…We also found “rigid network” modes in ice VIII and VII [2] and “isolated stretching” modes in ice XIV [12]. According to our series of investigations of ice phases, we identified two intrinsic categories of molecule vibrations in the translational band that constitute two sharp peaks [2,12,13,14,15]. In this paper, we confirm the presence of cluster vibrations in a much lower region of the translation band.…”

“…For theoretical investigations of vibrational modes, the most interesting results were those of Whale et al, who found exotic “rigid network” molecular vibrations in the translation band and “isolated stretching” modes of atomic vibrations in the stretching band [8]. We also found “rigid network” modes in ice VIII and VII [2] and “isolated stretching” modes in ice XIV [12]. According to our series of investigations of ice phases, we identified two intrinsic categories of molecule vibrations in the translational band that constitute two sharp peaks [2,12,13,14,15].…”

“…Most of them can be converted into hydrogen-disordered ice phase, in which the water molecules exhibit orientation disorder after heating. There are six known counterparts: Ih/XI, III/IX, V/XIII, VI/XV, VII/VIII, and XII/XIV [2]. The only exception is ice II, for which a hydrogen-disordered counterpart has not been observed.…”

Computing Investigations of Molecular and Atomic Vibrations of Ice IX

“…In addition, we noticed that Moberg et al used two methods to calculate the Raman spectra, which are many-body molecular dynamics (MB-MD) and normal mode (NM). 12 According to their work, two main Raman peaks were calculated at 3154 and 3243 cm –1 . Furthermore, our results were at 3177 and 3285 cm –1 .…”

Distinguishing ice β-XV from deep glassy ice VI: Raman spectroscopy

“…20,21 Raman spectra calculated for the antiferroelectric structure by DFT 14 are ''in essential agreement with experimental spectra of ice XV'', and so are the calculated structures for this structure by MB-MD. 22 This explanation leaves some room for speculation, which prompted Gasser et al to investigate the influence of pressure and cooling rate on H-ordering quantitatively and systematically. 1 By combining X-ray, differential scanning calorimetry (DSC), Ramanand dielectric relaxation spectroscopy experiments they identified a different cause for the complex behaviour that was not observed for any other ice polymorph before.…”