We present infrared and visible transient absorption measurements of 8′-apo-β-caroten-8′-al following one-photon excitation at 405 nm. An excess vibrational energy of ∼4000 cm−1 in the S2 state is created with 405 nm excitation. Relaxation from this vibronic region shows distinct relaxation pathways from those observed for 490 nm excitation which excites S2 near its origin. Infrared and visible transient absorption measurements show long-lived transient signals that persist longer than 1 ns. These transient spectra are identical to those observed in previous two-photon excitation measurements at 1275 nm. Our results are consistent with at least two minima on the S1 surface and a branched decay from hot S2 molecules to at least two of these minima.
