Disorder-Suppressed Vibrational Relaxation in Vapor-Deposited High-Density Amorphous Ice

Andrey Shalit, Chemistry, University of Zurich, Zurich, Switzerland
Fivos Perakis, Chemistry, University of Zurich, Zurich, Switzerland
Peter Hamm, Chemistry, University of Zurich, Zurich, Switzerland

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. High structural disorder and complete lack of spectral diffusion, intrinsic for the amorphous samples [1], allow one to observe variation in spectral properties of the uncoupled hydroxyl stretch vibration with hydrogen bond (HB) strength of surrounding water molecules. The vibrational lifetime (T₁) of the isolated OD stretch (10% HDO in H₂O) exhibits characteristic differences when comparing hexagonal (T₁=0.5ps), LDA (T₁=0.6ps) and HDA (T₁=1.6ps) ices under similar HB environment (i.e. same excitation frequency [2]), revealing reduced relaxation rate (by more than factor of 2) for the HDA. In addition the width of the 1-2 transition in HDA shows a reduced dependence on the excitation frequency when compared to LDA. We attribute these variations in the spectroscopic properties to the different local structures ─ in particular the presence of interstitial waters in HDA ice [3] ─ that cause different delocalization lengths of intermolecular phonon degrees of freedom. Temperature dependent measurements show that the vibrational lifetime of HDA ice decreases from 1.6 to 0.8 ps between 20 K and 40 K in a step-like manner, closely following its structural transformation to LDA ice around the same temperature [4].

[1] A. Shalit, F. Perakis and P. Hamm, J. Phys. Chem. B. 117 15512 (2013.

[2] R. Rey, K. Møller, and J. T. Hynes, J. Phys. Chem. A 106, 11993 (2002).

[3] J. L. Finney, A. Hallbrucker, I. Kohl, A. K. Soper, and D. T. Bowron, Phys. Rev. Lett. 88, 225503 (2002).

[4] P. Jenniskens and D. Blake, Science 265, 753 (1994)


Disorder-Suppressed Vibrational Relaxation in Vapor-Deposited High-Density Amorphous Ice Andrey Shalit, Chemistry, University of Zurich, Zurich, Switzerland Fivos Perakis, Chemistry, University of Zurich, Zurich, Switzerland Peter Hamm, Chemistry, University of Zurich, Zurich, Switzerland 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. High structural disorder and complete lack of spectral diffusion, intrinsic for the amorphous samples [1], allow one to observe variation in spectral properties of the uncoupled hydroxyl stretch vibration with hydrogen bond (HB) strength of surrounding water molecules. The vibrational lifetime (T₁) of the isolated OD stretch (10% HDO in H₂O) exhibits characteristic differences when comparing hexagonal (T₁=0.5ps), LDA (T₁=0.6ps) and HDA (T₁=1.6ps) ices under similar HB environment (i.e. same excitation frequency [2]), revealing reduced relaxation rate (by more than factor of 2) for the HDA. In addition the width of the 1-2 transition in HDA shows a reduced dependence on the excitation frequency when compared to LDA. We attribute these variations in the spectroscopic properties to the different local structures ─ in particular the presence of interstitial waters in HDA ice [3] ─ that cause different delocalization lengths of intermolecular phonon degrees of freedom. Temperature dependent measurements show that the vibrational lifetime of HDA ice decreases from 1.6 to 0.8 ps between 20 K and 40 K in a step-like manner, closely following its structural transformation to LDA ice around the same temperature [4]. [1] A. Shalit, F. Perakis and P. Hamm, J. Phys. Chem. B. 117 15512 (2013. [2] R. Rey, K. Møller, and J. T. Hynes, J. Phys. Chem. A 106, 11993 (2002). [3] J. L. Finney, A. Hallbrucker, I. Kohl, A. K. Soper, and D. T. Bowron, Phys. Rev. Lett. 88, 225503 (2002). [4] P. Jenniskens and D. Blake, Science 265, 753 (1994)

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