Vibrational spectra of solid samples were initially collected for the selected Cys isotopologues to verify the vibrational energy differences predicted by the DFT method. IR spectra of solidstate Cys-cabn and Cys-CABN are shown in Fig. , together with corresponding computational spectra for the isolated zwitterions. Raman spectra of the compounds, also correlated with corresponding computational spectra, are shown in Fig. . PED analysis of the observed vibrations are shown in Table and S5, for Cys-cabn and Cys-CABN, respectively. The assignments are in line with other works on the subject 101 . Experimental and theoretical spectra computed for the zwitterionic form of cysteine are in a good agreement, taking into account that we did not scale the computed vibrational energies. DFT-predicted shift of the νC-O signal was confirmed experimentally, with the value of -39 cm -1 based on the Raman spectra. The shift was also observed in the IR spectra, however as the bands were not resolved clearly, the estimation of the shift value is not viable.