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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.; Bačić, Zlatko

Authors

Anna Powers

Yohann Scribano

David Lauvergnat

Elsy Mebe

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

Zlatko Bačić



Abstract

© 2018 Author(s). We report a theoretical study of the frequency shift (redshift) of the stretching fundamental transition of an H 2 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) calculat ions of the coupled translation-rotation eigenstates are performed for H 2 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 H 2 and the water domains are treated as rigid. The 5D intermolecular potential energy surface (PES) of H 2 inside a hydrate domain is assumed to be pairwise additive. The H 2 -H 2 O pair interaction, represented by the 5D (rigid monomer) PES that depends on the vibrational state of H 2 , v=0 or v=1, is derived from the high-quality ab initio full-dimensional (9D) PES of the H 2 -H 2 O complex [P. Valiron et al., J. Chem. Phys. 129, 134306 (2008)]. The H 2 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 H 2 change very little with the domain size, unlike the H 2 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 H 2 O molecules in the first three complete hydration shells around H 2 .

Citation

Powers, A., Scribano, Y., Lauvergnat, D., Mebe, E., Benoit, D. M., & Bačić, Z. (2018). The effect of the condensed-phase environment on the vibrational frequency shift of a hydrogen molecule inside clathrate hydrates. The Journal of chemical physics, 148(14), 144304. https://doi.org/10.1063/1.5024884

Journal Article Type Article
Acceptance Date Mar 1, 2018
Online Publication Date Apr 9, 2018
Publication Date Apr 14, 2018
Deposit Date May 18, 2018
Publicly Available Date May 21, 2018
Journal Journal of Chemical Physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher AIP Publishing
Peer Reviewed Peer Reviewed
Volume 148
Issue 14
Article Number 144304
Pages 144304
DOI https://doi.org/10.1063/1.5024884
Public URL https://hull-repository.worktribe.com/output/794098
Publisher URL https://aip.scitation.org/doi/10.1063/1.5024884

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Copyright Statement
© Accepted version 2018 University of Hull; Published version 2019 AIP.






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