Figure shows 2D IR spectra of 2020 data in panels (A) and (D) for waiting times of 0.4 ps and 50 ps, and corresponding best-fit model spectra in panels (B) and (E). Qualitatively, the model appears consistent with the data in terms of shape and scale. A closer look at the residuals in panels (C) and (F), however, reveals the presence of a structured response at both waiting times. This residual response is roughly 10% of the amplitude of the total signal and is also present at similar magnitude in the 2021 data.