Resonance Raman investigation and semiempirical calculations of the bis(dicyanomethylene)croconate ion

Abstract The assignments of the optical and vibrational spectra of bis(dicyano)croconate are proposed on the basis of the resonance Raman excitation profiles as well as semi-empirical calculations at the AM1 and PM3 levels. The absorption band at 532 nm is assigned to a π → π * transition, involving a molecular orbital delocalized over the pseudo-oxocarbon ring, whereas the one at 442 nm is assigned to a transition localized at the CN moieties. The calculation of the excitation profiles was performed using the transform method with a simple model of displaced harmonic oscillators, and in addition, the same model was used to reproduce the π → π * absorption bandshape within the time-dependent formalism.