Figure 5.

Kinetics of β-carotene's S₀ C=C and S₁ C=C FSRS peak areas. (a) The S₀ C=C intensity at 1524 cm⁻¹ bleaches within the 80-fs cross-correlation (see inset) and recovers in 9 ± 1 ps. (b) The S₁ C=C integrated area at 1770 and 1798 cm⁻¹ rises to a maximum at a ∼2-ps time delay and then decays with a ∼9-ps lifetime. The early time behavior (b, inset) of the S₁ C=C peak is poorly fit by a simple three-state (dashed) kinetic model. The kinetics are better fit by a four-state model incorporating a 163 (±9) fs S₂ lifetime determined by transient absorption, a 200 (±20) fs intermediate lifetime, and an 8.7 (±0.9) ps S₁ lifetime (solid). Also shown in the inset is the actinic pump–Raman probe cross-correlation (80 fs, dot-dot-dashed) and the Raman pump envelope (800 fs, dot-dashed). The S₁ C=C data were collected in four different experiments (Δ,▽,□,○), plotted versus the corrected time delay (see text) and fit using a weighted nonlinear least-squares algorithm.