The empirical equilibrium structure of diacetylene

High-level quantum-chemical calculations are reported at the MP2 and CCSD(T) levels of theory for the equilibrium structure and the harmonic and anharmonic force fields of diacetylene, H-C = C-C C-H, The calculations were performed employing Dunning's hierarchy of correlation-consistent basis sets cc-pVXZ, cc-pCVXZ, and cc-pwCVXZ, as well as the ANO2 basis set of Almlof and Taylor. An empirical equilibrium structure based on experimental rotational constants for 13 isotopicspecies of diacetylene and computed zero-point vibrational corrections is determined (r(e)(emp) : r(C-H) = 1.0615 angstrom, r(C C) = 1.2085 angstrom, r(C-C) = 1.3727 angstrom) and in good agreement with the best theoretical structure (CCSD(T)/cc-pCV5Z: r(C-H) = 1.0617 angstrom, r(C C) = 1.2083 angstrom, r(C-C) = 1.3737 angstrom). In addition, the computed fundamental vibrational frequencies are compared with the available experimental data and found in satisfactory agreement. (C) 2008 Elsevier Inc. All rights reserved.