Ground‐State Structure of the Proton‐Bound Formate Dimer by Cold‐Ion Infrared Action Spectroscopy

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  • Daniel A. Thomas
    Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4–6 14195 Berlin Germany
  • Mateusz Marianski
    Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4–6 14195 Berlin Germany
  • Eike Mucha
    Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4–6 14195 Berlin Germany
  • Gerard Meijer
    Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4–6 14195 Berlin Germany
  • Mark A. Johnson
    Sterling Chemistry Laboratory Yale University 225 Prospect Street New Haven CT 06520 USA
  • Gert von Helden
    Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4–6 14195 Berlin Germany

Description

<jats:title>Abstract</jats:title><jats:p>The proton‐bound dicarboxylate motif, RCOO<jats:sup>−</jats:sup>⋅H<jats:sup>+</jats:sup>⋅<jats:sup>−</jats:sup>OOCR, is a prevalent chemical configuration found in many condensed‐phase systems. The proton‐bound formate dimer HCOO<jats:sup>−</jats:sup>⋅H<jats:sup>+</jats:sup>⋅<jats:sup>−</jats:sup>OOCH was studied utilizing cold‐ion IR action spectroscopy in the range 400–1800 cm<jats:sup>−1</jats:sup>. The spectrum obtained at ca. 0.4 K of ions captured in He nanodroplets was compared to that measured at ca. 10 K by photodissociation of Ar‐ion complexes. Similar band patterns are obtained by the two techniques that are consistent with calculations for a C<jats:sub>2</jats:sub> symmetry structure with a proton shared equally between the two formate moieties. Isotopic substitution experiments point to the nominal parallel stretch of the bridging proton appearing as a sharp, dominant feature near 600 cm<jats:sup>−1</jats:sup>. Multidimensional anharmonic calculations reveal that the bridging proton motion is strongly coupled to the flanking −COO<jats:sup>−</jats:sup> framework, an effect that is in line with the expected change in −C=O bond rehybridization upon protonation.</jats:p>

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