Electronic spectrum of dicyanoacetylene. 1. Calculations of the geometries and vibrations of ground and excited states of diacelylene, 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. Their performance encourages confidence in the predictions for the so far unanalyzed first singlet transition of NCCCCN.