Ab initio studies of the linear complex HC 3N⋯HC 3N

Abstract

Ab initio calculations using an STO-3G basis set have been performed to obtain the optimized geometry of the complex HC 3N⋯HC 3 N. A 6–31G basis set is then used at the STO-3G optimized geometry to estimate hydrogen bond energies, dipole moments, charge transfer effects, vibrational ground state rotational spectroscopic constants, and to analyze the perturbation of the N⋯H interaction on the IR intensity parameters of these atoms from their atomic polar tensors using the charge-charge flux-overlap (CCFO) model. These results support the conclusion from previous work, using the monomer experimental geometry and optimized r N⋯H bond distance, that the deformation modes are practically unaltered owing to the formation of the H bond and that the elements associated with the CN b and H b-C stretching modes increase substantially, mainly due to the charge flux term P zz (CF) in which charge transfer and polarization effects have important contributions. It is interesting that in this largest cyanopolyacetylene H-bonded complex of the series previously investigated, smaller basis sets and fixed monomer geometries yield similar trends in the physical interpretations as compared to the present more elaborate calculations using larger basis sets and a fully optimized geometry. This may be important regarding computational feasibility of larger complexes of the series under investigation, considering the large amount of computer time required to obtain optimized geometries of these complexes even at the STO-3G level.