Electronic Spectrum of Dicyanoacetylene. 1. Calculations of the Geometries and Vibrations of Ground and Excited States of Diacetylene, Cyanoacetylene, Cyanogen, Triacetylene, Cyanodiacetylene, and Dicyanoacetylene

The predictive reliability of calculations of the excitation energies, geometries, and vibration frequencies for the lower singlet states of NCCCCN is tested by similar calculations on well-characterized states of HCCCCH, HCCCN, NCCN, HCCCCCCH, and HCCCCCN. Their performance encourages confidence in the predictions for the so far unanalyzed first singlet transition of NCCCCN.