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Volume 212, 2018
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Spectral signatures of proton delocalization in H+(H2O)n=1−4 ions

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Couplings involving large amplitude vibrations in H+(H2O)n (n = 1–4) are explored using several theoretical approaches. These include harmonic treatments, analysis of harmonically coupled anharmonic oscillator (HCAO) models of the OH stretching vibrations, vibrational perturbation theory (VPT2) in internal coordinates, and diffusion Monte Carlo (DMC). It is found that couplings between shared proton stretches and HOH bends can lead to normal modes that are significantly mixed in character. Couplings between the various OH stretching vibrations are much weaker, and the OH stretches are well-described by harmonically coupled anharmonic oscillator models. Anharmonic couplings and the role of these large amplitude vibrations are further explored using DMC and VPT2. Based on the results of these calculations, it is found that all of the H+(H2O)n ions considered in this study display several different types of large amplitude vibrational motions even in their ground states. In the case of H7O3+, degenerate VPT2 calculations indicate that there are large couplings between the shared proton stretch and various lower frequency vibrations that correspond to motions that break the ionic hydrogen bonds. This leads to vibrational eigenstates that have contributions from several zero-order states.

Graphical abstract: Spectral signatures of proton delocalization in H+(H2O)n=1−4 ions

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Publication details

The article was received on 12 Jun 2018, accepted on 20 Jun 2018 and first published on 20 Jun 2018

Article type: Paper
DOI: 10.1039/C8FD00120K
Faraday Discuss., 2018,212, 443-466

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    Spectral signatures of proton delocalization in H+(H2O)n=1−4 ions

    L. C. Dzugan, R. J. DiRisio, L. R. Madison and A. B. McCoy, Faraday Discuss., 2018, 212, 443
    DOI: 10.1039/C8FD00120K

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