2D IR spectroscopy of high-pressure phases of ice

  • Halina Tran
    Department of Chemistry, University of Zürich 1 , Zürich, Switzerland
  • Ana V. Cunha
    Zernike Institute for Advanced Materials, University of Groningen 2 , Groningen, The Netherlands
  • Jacob J. Shephard
    Department of Chemistry, University College London 3 , 20 Gordon Street, London WC1H 0AJ, United Kingdom
  • Andrey Shalit
    Department of Chemistry, University of Zürich 1 , Zürich, Switzerland
  • Peter Hamm
    Department of Chemistry, University of Zürich 1 , Zürich, Switzerland
  • Thomas L. C. Jansen
    Zernike Institute for Advanced Materials, University of Groningen 2 , Groningen, The Netherlands
  • Christoph G. Salzmann
    Department of Chemistry, University College London 3 , 20 Gordon Street, London WC1H 0AJ, United Kingdom

抄録

<jats:p>We present experimental and simulated 2D IR spectra of some high-pressure forms of isotope-pure D2O ice and compare the results to those of ice Ih published previously [F. Perakis and P. Hamm, Phys. Chem. Chem. Phys. 14, 6250 (2012); L. Shi et al., ibid. 18, 3772 (2016)]. Ice II, ice V, and ice XIII have been chosen for this study, since this selection covers many aspects of the polymorphism of ice. That is, ice II is a hydrogen-ordered phase of ice, in contrast to ice Ih, while ice V and ice XIII are a hydrogen-disordered/ordered couple that shares essentially the same oxygen structure and hydrogen-bonded network. For the transmission 2D IR spectroscopy, a novel method had to be developed for the preparation of ultrathin films (1-2 μm) of high-pressure ices with good optical quality. We also simulated 2D IR spectra based on molecular dynamics simulations connected to a vibrational exciton picture. These simulations agree with the experimental results in a semi-quantitative manner for ice II, while the same approach failed for ice V and ice XIII. From the perspective of 2D IR spectroscopy, ice II appears to be more inhomogeneously broadened than ice Ih, despite its hydrogen-order, which we attribute to the fact that ice II is structurally more complex with four distinguishable hydrogen bonds that mix due to exciton coupling. Ice V and ice XIII, on the other hand, behave as expected with the hydrogen-disordered case (ice V) being more inhomogenously broadened. Furthermore, in all hydrogen-ordered forms (ice II and ice XIII), cross peaks could be identified in the anisotropic 2D IR spectrum, whose signs reveal the relative direction of the corresponding excitonic states.</jats:p>

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