The effect of the condensed-phase environment on the vibrational frequency shift of a hydrogen molecule inside clathrate hydrates

Anna Powers, Yohann Scribano, David Lauvergnat, Elsy Mebe, David M. Benoit, Zlatko Bacic

Research output: Contribution to journalArticle

Abstract

We report a theoretical study of the frequency shift (redshift) of the stretching fundamental transition of an H2 molecule confined inside the small dodecahedral cage of the structure II clathrate hydrate and its dependence on the condensed-phase environment. In order to determine how much the hydrate water molecules beyond the confining small cage contribute to the vibrational frequency shift, quantum five-dimensional (5D) calculations of the coupled translation-rotation eigenstates are performed for H2 in the v=0 and v=1 vibrational states inside spherical clathrate hydrate domains of increasing radius and a growing number of water molecules, ranging from 20 for the isolated small cage to over 1900. In these calculations, both H2 and the water domains are treated as rigid. The 5D intermolecular potential energy surface (PES) of H2 inside a hydrate domain is assumed to be pairwise additive. The H2-H2O pair interaction, represented by the 5D (rigid monomer) PES that depends on the vibrational state of H2, v=0 or v=1, is derived from the high-quality ab initio full-dimensional (9D) PES of the H2-H2O complex [P. Valiron et al., J. Chem. Phys. 129, 134306 (2008)]. The H2 vibrational frequency shift calculated for the largest clathrate domain considered, which mimics the condensed-phase environment, is about 10% larger in magnitude than that obtained by taking into account only the small cage. The calculated splittings of the translational fundamental of H2 change very little with the domain size, unlike the H2 j = 1 rotational splittings that decrease significantly as the domain size increases. The changes in both the vibrational frequency shift and the j = 1 rotational splitting due to the condensed-phase effects arise predominantly from the H2O molecules in the first three complete hydration shells around H2.

Original languageEnglish (US)
Article number144304
JournalJournal of Chemical Physics
Volume148
Issue number14
DOIs
StatePublished - Apr 14 2018

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clathrates
Vibrational spectra
Hydrates
hydrates
Potential energy surfaces
frequency shift
Hydrogen
Molecules
hydrogen
Water
molecules
potential energy
vibrational states
Hydration
water
Stretching
Monomers
confining
hydration
eigenvectors

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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The effect of the condensed-phase environment on the vibrational frequency shift of a hydrogen molecule inside clathrate hydrates. / Powers, Anna; Scribano, Yohann; Lauvergnat, David; Mebe, Elsy; Benoit, David M.; Bacic, Zlatko.

In: Journal of Chemical Physics, Vol. 148, No. 14, 144304, 14.04.2018.

Research output: Contribution to journalArticle

Powers, Anna ; Scribano, Yohann ; Lauvergnat, David ; Mebe, Elsy ; Benoit, David M. ; Bacic, Zlatko. / The effect of the condensed-phase environment on the vibrational frequency shift of a hydrogen molecule inside clathrate hydrates. In: Journal of Chemical Physics. 2018 ; Vol. 148, No. 14.
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