Saturation effects on ultraviolet resonance Raman intensities: Excimer/YAG laser comparison and aromatic amino acid cross‐sections

Abstract

AbstractSubstantial saturation effects are noted for resonance Raman (RR) bands of the aromatic residues in cytochrome c (excited at 230 nm) with an H2 Raman‐shifted YAG or a frequency‐doubled excimer‐pumped dye laser. At a given average power, saturation is much lower for excimer than for YAG excitation because of the longer pulse and higher repetition rate of the excimer laser. The signal quality at low average power is significantly higher for the excimer‐excited spectra. Ultraviolet RR cross‐sections have been redetermined for aqueous phenylalanine, tyrosine and tryptophan at a series of wavelengths from 240 to 192 nm. The excimer laser was used at 209 nm and longer wavelengths, and in addition deconvolution techniques were applied to better define the individual RR bands. These improvements led to quantitative changes in the cross‐section values from those reported previously, but the interpretation of the excitation profiles in terms of excited‐state properties of the aromatic residues remains unchanged.