Weak interactions in ion–ligand complexes of C3H +3 isomers: competition between H-bound and C-bound structures in c-C3H +3·L and H2CCCH+·L (L = Ne, Ar, N2, CO2, and O2)

Abstract

Explicitly correlated coupled cluster theory at the CCSD(T)-F12x level (T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys.127, 221106, 2007) has been employed to study structures and vibrations of complexes of type c-C₃H⁺₃·L and H₂C₃H⁺·L (L = Ne, Ar, N₂, CO₂, and O₂). Both cations have different binding sites, allowing for the formation of weak to moderately strong hydrogen bonds as well as “C-bound” or “π-bound” structures. In contrast to previous expectations, the energetically most favourable structures of all H₂C₃H⁺·L complexes investigated are “C-bound”, with the ligand bound to the methylenic carbon atom. The theoretical predictions enable a more detailed interpretation of infrared photodissociation (IRPD) spectra than was possible hitherto. In particular, the bands observed in the range 3238–3245 cm⁻¹ (D. Roth and O. Dopfer, Phys. Chem. Chem. Phys.4, 4855, 2002) are assigned to essentially free acetylenic CH stretching vibrations of the propargyl cation in “C-bound” H₂C₃H⁺·L complexes.