Spectroscopic studies and normal coordinate analysis of bilirubin

The infrared spectrum of bilirubin has been recorded in the spectral region 200-4000 cm(-1). The Raman spectrum has also been recorded using the second harmonic (530 nm) radiation of a 200 mW Nd-YAG laser. In order to confirm the vibrational assignment of the bands obtained from experimental observation, a normal coordinate analysis has been carried out using the semi-empirical AM1 method through MOPAC 5.1 computer program. Electronic absorption spectrum of bilirubin dissolved in CHCl3 has been recorded in the spectral region 300-600 nm. A broad spectrum is observed with peak maxima at 454.2 nm. The photoacoustic spectrum of this molecule (in the powder form) has also been recorded for the first time which shows certain discrete features.