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, HCCCCH. 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 Almlöf and Taylor. An empirical equilibrium structure based on experimental rotational constants for 13 isotopic species of diacetylene and computed zero-point vibrational corrections is determined (reemp:rCH=1.0615Å,rCC=1.2085Å,rCC=1.3727Å) and in good agreement with the best theoretical structure (CCSD(T)/cc-pCV5Z: rCH=1.0617Å, rCC=1.2083Å, rCC=1.3737Å). In addition, the computed fundamental vibrational frequencies are compared with the available experimental data and found in satisfactory agreement.