Evolution of Hydrogen Dynamics in Amorphous Ice with Density.
The single-particle dynamics of hydrogen atoms in several of the amorphous ices are reported using a combination of deep inelastic neutron scattering (DINS) and inelastic neutron scattering (INS). The mean kinetic energies of the hydrogen nuclei are found to increase with increasing density, indicating the weakening of hydrogen bonds as well as a trend toward steeper and more harmonic hydrogen vibrational potential energy surfaces. DINS shows much more pronounced changes in the O-H stretching component of the mean kinetic energy going from low- to high-density amorphous ices than indicated by INS and Raman spectroscopy. This highlights the power of the DINS technique to retrieve accurate ground-state kinetic energies beyond the harmonic approximation. In a novel approach, we use information from DINS and INS to determine the anharmonicity constants of the O-H stretching modes. Furthermore, our experimental kinetic energies will serve as important benchmark values for path-integral Monte Carlo simulations.
†Dipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy.
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Parmentier
‡Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.|§Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom.
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Shephard
†Dipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy.
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Romanelli
†Dipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy.|∥CNR-IPCF Sezione di Messina, Viale F. Stagno D'Alcontres 37, 98158 Messina, Italy.
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Senesi
‡Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
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Salzmann
†Dipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy.|∥CNR-IPCF Sezione di Messina, Viale F. Stagno D'Alcontres 37, 98158 Messina, Italy.
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Andreani
Raman spectroscopy; deep inelastic neutron scattering; hydrogen bonding; ice; inelastic neutron scattering