Figure 3.

Femtosecond TA spectra of the high-salt type 1 solution, primarily composed of type 1 tetramer structures, collected with pump wavelengths of 555 and 660 nm at pump fluences of 26 and 18 μJ/cm², respectively. (a,e) Surface plots. Vertical dashed lines indicate kinetics traces that are plotted in panels (d,h), respectively. (b,f) Selected TA spectra for each pump wavelength. Time delays are indicated in the legend. (c,g) Kinetic schemes used for GTA. The rate constants associated with specific components are reported as inverse time constants. In the case of panel (g), all rate constants were fixed except for the rate constant associated with the fourth component (or SAS₄). (d,h) Selected TA kinetics, normalized to their maximum amplitude near the time origin of the measurement. Data are shown as circles, while fits are shown as solid lines. Panel (d) displays TA kinetics at a probe wavelength of 561 nm, which corresponds to the GSB of the type 1 tetramer structure; the inset of panel (d) displays TA kinetics taken at probe wavelengths of 561 and 583 nm corresponding to the GSB and ESA, respectively, of the type 1 tetramer structure. Panel (h) displays TA kinetics at a probe wavelength of 561 nm, which corresponds primarily to the GSB of the type 1 tetramer structure, and at probe wavelengths of 635 and 667 nm, which correspond primarily to the ESA and GSB, respectively, of the duplex dimer structure.