Fig. 4.

Temporal changes of integrated intensity of the 1620-cm⁻¹ and Y9a bands relative to the intensity in the probe-only spectrum. It should be noted that the intensity change of the band at 1620 cm⁻¹ mainly arises from intensity change of Y8a band with a smaller contribution from intensity change of W1 band. The solid lines are fits using a sum of two exponential functions of the form A[1 − exp(−t/τ_decay)] + B[exp(−t/τ_rise) − 1] convoluted with the instrument response function (dashed line). The fit line for the 1,620-cm⁻¹ band was obtained with the parameters of τ_decay = 1.9 ± 0.9 ps, τ_rise = 7.3 ± 1.4 ps, A = 0.21 ± 0.03, and B = 0.19 ± 0.03. The fit line for the Y9a band was obtained with the parameters of τ_decay = 2.0 ± 0.8 ps, τ_rise = 8.0 ± 3.6 ps, A = 0.19 ± 0.03, and B = 0.18 ± 0.03. The lower panel shows a close-up of the curve in the early time region of the upper panel.