Communication: Disorder-suppressed vibrational relaxation in vapor-deposited high-density amorphous ice

Abstract

We apply two-dimensional infrared spectroscopy to differentiate between the two polyamorphous forms of glassy water, low-density (LDA) and high-density (HDA) amorphous ices, that were obtained by slow vapor deposition at 80 and 11 K, respectively. Both the vibrational lifetime and the bandwidth of the 1-2 transition of the isolated OD stretch vibration of HDO in H 2 O exhibit characteristic differences when comparing hexagonal (Ih), LDA, and HDA ices, which we attribute to the different local structures -in particular the presence of interstitial waters in HDA ice -that cause different delocalization lengths of intermolecular phonon degrees of freedom. Moreover, temperature dependent measurements show that the vibrational lifetime closely follows the structural transition between HDA and LDA phases.

Vibrational Spectroscopy and Dynamics of Water

“…The latter is believed to be responsible for the minor diagonal elongation of the 2D-IR ground-state signal (blue lobe) shown in Figure b, as confirmed by the simulations . Furthermore, the 2D-IR line shape of ice Ih features a distinct line shape asymmetry between ground-state (blue lobe) and excited-state contributions (red lobe), which is also partially present in the LDA and HDA ices (Figure c,d). , This line shape asymmetry has been also reported for the OH stretch of HOD/D 2 O of liquid water and ice Ih, ,, where it appears much more pronounced than in the OD stretch case. This feature strongly indicates that the excited state in isotope-diluted ice is spatially delocalized and thus samples many different environments, resulting in a broad range of excitation frequencies.…”

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

“…In conclusion, as the hydrogen bonds weaken with increasing density, the effective potential becomes less and less anharmonic and its shape becomes similar to the shapes inferred from other spectroscopic techniques within the harmonic assumption [38]. This is consistent with recent findings on LDA and HDA from 2D IR spectroscopy [46].…”

2D IR spectroscopy of high-pressure phases of ice

“…[29][30][31] If a spectroscopic transition is inhomogenously broadened, for example, due to hydrogen-disorder or presence of different hydrogen-bond environments, the corresponding 2D IR peak will be elongated along the diagonal. While such an elongation could be observed for isotope-diluted ice Ih both in experiment 19 and simulation, 18 the 2D IR spectra of neat ice Ih did not reveal any signature of inhomogeneous broadening, 20 suggesting a strong exchange narrowing effect. 18 This exchange narrowing arises from the previously discussed excitonic coupling between local vibrations leading to the formation of delocalized states which essentially report on an average of the frequencies of the involved local vibrations.…”

“…The hydrogen-ordered phases of ice represent an important class of materials in this respect since they are the only forms of condensed water for which the spectroscopic selection rules are firmly defined 16 and consequently, coupling processes are expected to take place over very long distances. In order to obtain a more complete understanding of the spectroscopy of condensed water phases, multi-dimensional spectroscopic techniques have been recently employed to study isotope-diluted [17][18][19] and isotope-pure ice Ih 20,21 both experimentally and theoretically. 2D IR spectroscopy extends conventional IR absorption spectroscopy, which is also sometimes called linear or 1D spectroscopy, by an extra frequency dimension.…”