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

The assignments of the optical and vibrational spectra of bis(dicyano)croco nate are proposed on the basis of the resonance Raman excitation profiles a s well as semi-empirical calculations at the AM1 and PM3 levels. The absorp tion band at 532 nm is assigned to a pi-->pi* transition, involving a molec ular orbital delocalized over the pseudo-oxocarbon ring, whereas the one at 442 nm is assigned to a transition localized at the CN moieties, The calcu lation 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 pi-->pi* absorption bandshape within the time-dependent formalism., (C) 1999 Elsevier Science B.V. All rights re served.