Deep-ultraviolet Raman excitation profiles and vibronic scattering mechanisms of phenylalanine, tyrosine, and tryptophan

Raman cross sections for excitation at wavelengths between 240 and 192 nm have been determined for resonance-enhanced ring modes of phenylalanine (Phe), tyrosine (Tyr), tyrosinate (Tyr super(-)), and tryptophan (Trp) and for the breathing mode of SO sub(4) super(2) super(-) and the symmetric OH stretching mode of H sub(2)O. The SO sub(4) super(2) super(-) and H sub(2)O bands, which are frequently used for relative intensity measurements, show strong preresonance enhancement at wavelengths below 220 nm, requiring large corrections to convert relative to absolute intensities. The aromatic amino acid intensity measurements were obtained with laser power levels in the linear regime and appear not to be influenced by saturation effects or photochemical transients.