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Intramolecular stretching vibrational states and frequency shifts of (H2)2 confined inside the large cage of clathrate hydrate from an eight-dimensional quantum treatment using small basis sets

Felker, Peter M.; Lauvergnat, David; Scribano, Yohann; Benoit, David M.; Bačić, Zlatko

Authors

Peter M. Felker

David Lauvergnat

Yohann Scribano

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Dr David Benoit D.Benoit@hull.ac.uk
Senior Lecturer in Molecular Physics and Astrochemistry

Zlatko Bačić



Abstract

We report the results of calculations pertaining to the HH intramolecular stretching fundamentals of (p-H2)2 encapsulated in the large cage of structure II clathrate hydrate. The eight-dimensional (8D) quantum treatment assumes rotationless (j = 0) H2 moieties and a rigid clathrate structure but is otherwise fully coupled. The (H2)2-clathrate interaction is constructed in a pairwise-additive fashion, by combining the ab initio H2-H2O pair potential for flexible H2 and rigid H2O [D. Lauvergnat et al., J. Chem. Phys. 150, 154303 (2019)] and the six-dimensional (6D) H2-H2 potential energy surface [R. J. Hinde, J. Chem. Phys. 128, 154308 (2008)]. The calculations are performed by first solving for the eigenstates of a reduced-dimension 6D "intermolecular" Hamiltonian extracted from the full 8D Hamiltonian by taking the H2 moieties to be rigid. An 8D contracted product basis for the solution of the full problem is then constructed from a small number of the lowest-energy 6D intermolecular eigenstates and two discrete variable representations covering the H2-monomer internuclear distances. Converged results are obtained already by including just the two lowest intermolecular eigenstates in the final 8D basis of dimension 128. The two HH vibrational stretching fundamentals are computed for three hydrate domains having an increasing number of H2O molecules. For the largest domain, the two fundamentals are found to be site-split by ∼0.5 cm-1 and to be redshifted by about 24 cm-1 from the free-H2 monomer stretch frequency, in excellent agreement with the experimental value of 26 cm-1. A first-order perturbation theory treatment gives results that are nearly identical to those of the 8D quantum calculations.

Citation

Felker, P. M., Lauvergnat, D., Scribano, Y., Benoit, D. M., & Bačić, Z. (2019). Intramolecular stretching vibrational states and frequency shifts of (H2)2 confined inside the large cage of clathrate hydrate from an eight-dimensional quantum treatment using small basis sets. The Journal of chemical physics, 151(12), https://doi.org/10.1063/1.5124051

Journal Article Type Article
Acceptance Date Sep 9, 2019
Online Publication Date Sep 30, 2019
Publication Date Sep 30, 2019
Deposit Date Oct 5, 2019
Publicly Available Date Oct 1, 2020
Journal The Journal of chemical physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher AIP Publishing
Peer Reviewed Peer Reviewed
Volume 151
Issue 12
Article Number 124311
DOI https://doi.org/10.1063/1.5124051
Keywords Physical and Theoretical Chemistry; General Physics and Astronomy
Public URL https://hull-repository.worktribe.com/output/2853599
Publisher URL https://aip.scitation.org/doi/10.1063/1.5124051
Additional Information Received: 2019-08-12; Accepted: 2019-09-09; Published: 2019-09-30

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Copyright Statement
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 151, 124311 (2019) and may be found at https://doi.org/10.1063/1.5124051.





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