Fig. 4: Photoinduced spectral changes associated with the fast (picoseconds) and slow (nanoseconds to microseconds) evolving species after the photoexcitation of the isolated carbonmonoxy chains of human HbCO.

a, b The representative transient mid-IR absorption spectra associated with the intermediate species evolving in the first 100 picoseconds after the photoexcitation (solid lines). The ground-state FTIR absorption spectrum normalized to an arbitrary value is shown as the short-dash line for comparison. c, d The representative transient mid-IR spectra associated with the intermediate species evolving over a timescale ranging from nanoseconds to hundreds of microseconds. The transient IR spectra were obtained for the isolated α chains (a, c) and the isolated β chains (b, d). The pump-probe delays are color-coded in the transient spectra. The arrows indicate the time evolution of the signal. The shown transient spectra correspond to the magic angle relative polarization between the pump and the probe beams. Similar spectra were obtained for the other two (parallel and perpendicular) polarization conditions. Note the difference in the time range for the data shown in (a, b) vs. (c, d). Source data are provided as a Source Data file.