Microscopic Study of Proton Kinetic Energy Anomaly for Nanoconfined Water

Mohd Moid; Yacov Finkelstein; Raymond Moreh; Prabal K. Maiti

doi:10.1021/acs.jpcb.9b08667

Microscopic Study of Proton Kinetic Energy Anomaly for Nanoconfined Water

Mohd Moid, Yacov Finkelstein, Raymond Moreh, Prabal K. Maiti

Department of Physics

Research output: Contribution to journal › Article › peer-review

13 Scopus citations

Abstract

The reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), constitute a longstanding problem related to proton dynamics in hydrogen-bonded systems. A considerable number of theoretical attempts to explain these anomalies have failed. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, D_CNT, by classical molecular dynamics (MD) simulation using the TIP4P-2005f water model. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5 K for D_CNT < ∼12 Å, while absent for larger diameters. The results also reveal very significant blue and red shifts of the stretching and bending modes, respectively, compared to those in bulk ice, in agreement with experiment.

Original language	English
Pages (from-to)	190-198
Number of pages	9
Journal	Journal of Physical Chemistry B
Volume	124
Issue number	1
DOIs	https://doi.org/10.1021/acs.jpcb.9b08667
State	Published - 9 Jan 2020

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Surfaces, Coatings and Films
Materials Chemistry

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title = "Microscopic Study of Proton Kinetic Energy Anomaly for Nanoconfined Water",

abstract = "The reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), constitute a longstanding problem related to proton dynamics in hydrogen-bonded systems. A considerable number of theoretical attempts to explain these anomalies have failed. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, DCNT, by classical molecular dynamics (MD) simulation using the TIP4P-2005f water model. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5 K for DCNT < ∼12 {\AA}, while absent for larger diameters. The results also reveal very significant blue and red shifts of the stretching and bending modes, respectively, compared to those in bulk ice, in agreement with experiment.",

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AU - Finkelstein, Yacov

AU - Moreh, Raymond

AU - Maiti, Prabal K.

PY - 2020/1/9

Y1 - 2020/1/9

N2 - The reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), constitute a longstanding problem related to proton dynamics in hydrogen-bonded systems. A considerable number of theoretical attempts to explain these anomalies have failed. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, DCNT, by classical molecular dynamics (MD) simulation using the TIP4P-2005f water model. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5 K for DCNT < ∼12 Å, while absent for larger diameters. The results also reveal very significant blue and red shifts of the stretching and bending modes, respectively, compared to those in bulk ice, in agreement with experiment.

AB - The reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), constitute a longstanding problem related to proton dynamics in hydrogen-bonded systems. A considerable number of theoretical attempts to explain these anomalies have failed. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, DCNT, by classical molecular dynamics (MD) simulation using the TIP4P-2005f water model. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5 K for DCNT < ∼12 Å, while absent for larger diameters. The results also reveal very significant blue and red shifts of the stretching and bending modes, respectively, compared to those in bulk ice, in agreement with experiment.

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Microscopic Study of Proton Kinetic Energy Anomaly for Nanoconfined Water

Abstract

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