Normal coordinate analysis of bilirubin vibrational spectra: effects of intramolecular hydrogen bonding

Ah&act-Normal coordinate analyses are presented for half-bilirnbin molecules. Calculations for the A-B pyrromethenone include intramolecular hydrogen bonds, while those for the C-D chromophore exclude intramolecular hydrogen bonds. Valence force-held parameters have been optimized to correlate closely with the IR and Raman spectra of the target molecules. The results of the calculations are compared with the spectra of bilirnbin IXa and various model compounds in the solid state and solution.