Please do not adjust margins characteristics, except that the probe was then attenuated by 4 orders of magnitude using a neutral density filter. The pump arrival time was changed relative to the probe using a pair of rotating optical flats, which allowed for up to ∼800 fs of delay with sub-fs precision. The intensity of the probe was detected and spectrally resolved using a spectrograph (Shamrock SR303i, Andor) and CCD camera (Newton 970, Andor). The pump was modulated with a chopper wheel to provide data as the change in probe intensity, ∆I. Samples were measured in a 1-mm pathlength cuvette (21-Q-1, Starna Cells) and diluted in acetone until the maximum absorbance was below 0.6.