Matrix-isolation and computational study of the HKrCCH•••HCCH complex

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.