Fig. 1: Static and differential sulfur K-edge absorption spectra of L-cystine with TD-DFT-calculated transitions.

Error bars represent standard deviations of the 600 measurement values acquired in 10 s from which each data point was calculated. A Static spectrum of L-cystine (1, black) with calculated lowest vertical excitation energies (blue sticks) and corresponding isosurface plots of the difference electron attachment densities (turquoise). B Differential spectra taken 0.3 ps, 3 ps and 10 ps after 267-nm excitation (black). Calculated transitions for the parent ion are shown in blue, for the thiyl radical (2) in orange and for the perthiyl radical (3) in purple. Isosurface plots (turquoise) show the beta attachment densities of the dominant excitation. The absorption changes are normalized to the K-edge height of L-cystine, i.e. the thiyl radical peak absorption at 300 fs amounts to 17 % of the parent molecule’s K-edge jump. Vertical gray lines indicate the energies at which delay scans were recorded (c.f. Figure 3). Source data are provided as a Source Data file.