Fig. 2.

Observed and calculated Raman and ROA spectra of PYP whose chromophore is unlabeled (black) and ¹³C8 labeled (red). (A) The observed Raman spectra. (B) The calculated Raman spectra. (C) The observed and (D) calculated ¹³C minus ¹²C difference Raman spectra. (E) The observed ROA spectra. (F) The calculated ROA spectra. (G) The observed and (H) calculated ¹³C minus ¹²C difference ROA spectra. PYP samples were dissolved in 10 mM Tris⋅HCl, pH 7.4, and the sample concentration was 4−5 mM. The spectra were obtained with 785-nm excitation (∼200 mW). The calculated spectra were based on model 1, and Gaussian band shapes with a 10 cm⁻¹ width were used except a 20 cm⁻¹ width for the highest band at 1,539 cm⁻¹. Raman and ROA intensities for the highest intensity bands were reduced by a factor of 2 (1,319, 1,314, 1,310, 1,268, 1,266, and 1,259 cm⁻¹) or 10 (1,633, 1,628, and 1,539 cm⁻¹) to make the other bands visible in the figure. The ROA spectra are magnified by a factor of 2,000.