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Competition between weak OH·π and CH·O hydrogen bonds : THz spectroscopy of the C2H2 - H2O and C2H4 - H2O complexes

Andersen, J. LU ; Heimdal, J. LU ; Nelander, B. LU and Wugt Larsen, R. LU (2017) In Journal of Chemical Physics 146(19).
Abstract

THz absorption spectra have been recorded for the weakly bound molecular complexes of H2O with C2H4 and C2H2 embedded in cryogenic neon matrices at 2.8 K. The observation and assignment of a large-amplitude acceptor OH librational mode of the C2H2 - H2O complex at 145.5 cm−1 confirms an intermolecular CH⋯O hydrogen-bonded configuration of C2v symmetry with the H2O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C2H4 - H2O complex at 255.0 and 187.5 cm−1, respectively, confirms an... (More)

THz absorption spectra have been recorded for the weakly bound molecular complexes of H2O with C2H4 and C2H2 embedded in cryogenic neon matrices at 2.8 K. The observation and assignment of a large-amplitude acceptor OH librational mode of the C2H2 - H2O complex at 145.5 cm−1 confirms an intermolecular CH⋯O hydrogen-bonded configuration of C2v symmetry with the H2O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C2H4 - H2O complex at 255.0 and 187.5 cm−1, respectively, confirms an intermolecular OH⋯π hydrogen-bonded configuration with the H2O subunit acting as the hydrogen bond donor to the π-cloud of C2H4. A (semi)-empirical value for the change of vibrational zero-point energy of 4.0-4.1 kJ mol−1 is proposed and the combination with quantum chemical calculations at the CCSD(T)-F12b/aug-cc-pVQZ level provides a reliable estimate of 7.1 ± 0.3 kJ mol−1 for the dissociation energy D0 of the C2H4 - H2O complex. In addition, tentative assignments for the two strongly infrared active OH librational modes of the ternary C2H4 - HOH - C2H4 complex having H2O as a doubly OH·π hydrogen bond donor are proposed at 213.6 and 222.3 cm−1. The present findings demonstrate that the relative stability of the weak hydrogen bond motifs is not entirely rooted in differences of electronic energy but also to a large extent by differences in the vibrational zero-point energy contributions arising from the class of large-amplitude intermolecular modes.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Chemical Physics
volume
146
issue
19
publisher
American Institute of Physics
external identifiers
  • scopus:85019227309
  • wos:000401776300015
ISSN
0021-9606
DOI
10.1063/1.4983293
language
English
LU publication?
yes
id
3807c7c3-ebdf-4f1d-831d-8e22c4898cea
date added to LUP
2017-05-30 07:43:19
date last changed
2017-09-18 11:37:58
@article{3807c7c3-ebdf-4f1d-831d-8e22c4898cea,
  abstract     = {<p>THz absorption spectra have been recorded for the weakly bound molecular complexes of H<sub>2</sub>O with C<sub>2</sub>H<sub>4</sub> and C<sub>2</sub>H<sub>2</sub> embedded in cryogenic neon matrices at 2.8 K. The observation and assignment of a large-amplitude acceptor OH librational mode of the C<sub>2</sub>H<sub>2</sub> - H<sub>2</sub>O complex at 145.5 cm<sup>−1</sup> confirms an intermolecular CH⋯O hydrogen-bonded configuration of C<sub>2v</sub> symmetry with the H<sub>2</sub>O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C<sub>2</sub>H<sub>4</sub> - H<sub>2</sub>O complex at 255.0 and 187.5 cm<sup>−1</sup>, respectively, confirms an intermolecular OH⋯π hydrogen-bonded configuration with the H<sub>2</sub>O subunit acting as the hydrogen bond donor to the π-cloud of C<sub>2</sub>H<sub>4</sub>. A (semi)-empirical value for the change of vibrational zero-point energy of 4.0-4.1 kJ mol<sup>−1</sup> is proposed and the combination with quantum chemical calculations at the CCSD(T)-F12b/aug-cc-pVQZ level provides a reliable estimate of 7.1 ± 0.3 kJ mol<sup>−1</sup> for the dissociation energy D<sub>0</sub> of the C<sub>2</sub>H<sub>4</sub> - H<sub>2</sub>O complex. In addition, tentative assignments for the two strongly infrared active OH librational modes of the ternary C<sub>2</sub>H<sub>4</sub> - HOH - C<sub>2</sub>H<sub>4</sub> complex having H<sub>2</sub>O as a doubly OH·π hydrogen bond donor are proposed at 213.6 and 222.3 cm<sup>−1</sup>. The present findings demonstrate that the relative stability of the weak hydrogen bond motifs is not entirely rooted in differences of electronic energy but also to a large extent by differences in the vibrational zero-point energy contributions arising from the class of large-amplitude intermolecular modes.</p>},
  articleno    = {194302},
  author       = {Andersen, J. and Heimdal, J. and Nelander, B. and Wugt Larsen, R.},
  issn         = {0021-9606},
  language     = {eng},
  month        = {05},
  number       = {19},
  publisher    = {American Institute of Physics},
  series       = {Journal of Chemical Physics},
  title        = {Competition between weak OH·π and CH·O hydrogen bonds : THz spectroscopy of the C<sub>2</sub>H<sub>2</sub> - H<sub>2</sub>O and C<sub>2</sub>H<sub>4</sub> - H<sub>2</sub>O complexes},
  url          = {http://dx.doi.org/10.1063/1.4983293},
  volume       = {146},
  year         = {2017},
}