Browsing by Subject "NONCOVALENT INTERACTIONS"

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  • Leverentz, Hannah R.; Siepmann, J. Ilja; Truhlar, Donald G.; Loukonen, Ville; Vehkamäki, Hanna (2013)
  • Wannarit, Nanthawat; Pakawatchai, Chaveng; Mutikainen, Ilpo; Costa, Ramon; Moreira, Iberio de P. R.; Youngme, Sujittra; Illas, Francesc (2013)
  • Willmann, Knut; Vent-Schmidt, Thomas; Rasanen, Markku; Riedel, Sebastian; Khriachtchev, Leonid (2015)
    The HKrCCH center dot center dot center dot HCCH complex is identified in a Kr matrix with the H-Kr stretching bands at 1316.5 and 1305 cm(-1). The monomer-to-complex shift of the H-Kr stretching mode is about +60 cm(-1), which is significantly larger than that reported previously for the HXeCCH center dot center dot center dot HCCH complex in a Xe matrix (about +25 cm(-1)). The HKrCCH center dot center dot center dot HCCH complex in a Kr matrix is formed at similar to 40 K via the attachment of mobile acetylene molecules to the HKrCCH monomers formed at somewhat lower annealing temperatures upon thermally-induced mobility of H atoms (similar to 30 K). The same mechanism was previously proposed for the formation of the HXeCCH center dot center dot center dot HCCH complex in a Xe matrix. The assignment of the HKrCCH center dot center dot center dot HCCH complex is fully supported by the quantum chemical calculations. The experimental shift of the H-Kr stretching mode is comparable with the computational predictions (+46.6, +66.0, and +83.2 cm(-1) at the B3LYP, MP2, and CCSD(T) levels of theory, respectively), which are also bigger that the calculated shift in the HXeCCH center dot center dot center dot HCCH complex. These results confirm that the complexation effect is bigger for less stable noble-gas hydrides.
  • Duarte, Luis; Khriachtchev, Leonid (2017)
    We report on the identification of the complexes of two noble-gas hydrides, HXeCCXeH and HXeCC, with acetylene. These complexes were prepared by photolysis (250 nm) and annealing (55-65 K) of HCCH/Xe matrices. The experimentally observed monomer-to-complex shifts of the H-Xe stretching modes of the HXeCCXeH center dot center dot center dot HCCH (about +17 cm(-1)) and HXeCC center dot center dot center dot HCCH complexes (from +20 to +46 cm(-1)) indicate the stabilization of the H-Xe bond relatively to the monomers. The CCSD/cc-pVTZ calculations predict two structures for each complex. The HXeCCXeH center dot center dot center dot HCCH complex has quasi T-shaped and linear structures, with the H-Xe stretching modes blue-shifted and red-shifted by about +27 and -9 cm(-1), respectively. The HXeCC center dot center dot center dot HCCH complex has bent and T-shaped structures, with the H-Xe stretching modes blue-shifted by about +46 and +42 cm(-1), respectively. Based on the calculations, the experimental bands of the HXeCCXeH center dot center dot center dot HCCH and HXeCC center dot center dot center dot HCCH complexes are assigned to the quasi T-shaped and bent structures, respectively. Complexes of an open-shell noble-gas hydride and of a molecule with two noble-gas atoms are reported for the first time.
  • Ryazantsev, Sergey V.; Tyurin, Daniil A.; Feldman, Vladimir I.; Khriachtchev, Leonid (2017)
    We report on the preparation and vibrational characterization of the C2H3 center dot center dot center dot CO2 complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HC3OOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO2, without the presence of either CO2 or C2H3 monomers. The absorption bands corresponding to the nu(5)(C2H3), nu(7)(C2H3), nu(8)(C2H3), nu(2)(CO2), and nu(3)(CO2) modes of the C2H3 center dot center dot center dot CO2 complex were detected experimentally. The calculations at the UCCSD(T)/L2a level of theory predict two structures of the C2H3 center dot center dot center dot CO2 complex with C-s and C-1 symmetries and interaction energies of -1.92 and -5.19 kJ mol(-1). The harmonic vibrational frequencies of these structures were calculated at the same level of theory. The structural assignment of the experimental species is not straightforward because of rather small complexation-induced shifts and matrix-site splitting of the bands (for both complex and monomers). We conclude that the C-1 structure is the most probable candidate for the experimental C2H3 center dot center dot center dot O-2 complex based on the significant splitting of the bending vibration of CO2 and on the energetic and structural considerations. Published by AIP Publishing.