Fig. 5.

Transient absorption (TA) measurements of retinal protonated Schiff-base (RPSB) in the gas phase at 300 and 100 K. The TA data are shown as a function of variable probe wavelength (fixed 600 nm pump). The grey area shows the ground-state absorption profile at 300 K (one-photon spectrum). The transient absorption spectra at asymptotic long times (10–500 ps) correspond to absorption from a hot ground state, peaking at 620 nm. The excited-state absorption in the red part disappears with time concomitantly with a rise of the ground-state absorption with a lifetime, which strongly depends on temperature. Three major peaks at 720, 660, and 620 nm are seen at both temperatures. See discussion in the text