Fig. 2: Time-resolved transient mid-IR absorption changes of the isolated carbonmonoxy chains of human HbCO in the region of ground-state bleach.

a, d The representative spectra detected on the 2–100 ps timescale after the photoexcitation. b, e Zoomed-in spectra shown in (a) and (d), respectively, in the high-frequency region of the negative band centered at ~1950 cm^–1. c, f The representative spectra detected in the time range from 100 ps to hundreds of microseconds. The spectra were obtained for the isolated carbonmonoxy α chains (a–c) and carbonmonoxy β chains (d–f). The arrows indicate the time evolution of the signal. The spectra shown correspond to the magic angle relative polarization between the pump and the probe beams. The time-resolved mid-IR measurements were repeated 4 times for each sample. In a single measurement, typically 75 time delay points were used. Each time-resolved mid-IR spectrum shown corresponds to 150,000 averaged laser shots. Conditions: 50 mM Tris buffer, pD 8.2, at 19 °C. Concentrations of the carbonmonoxy α and β chains were 3.0 and 4.0 mM in heme, respectively. Excitation wavelength, λ_exc = 543 nm. Source data are provided as a Source Data file.