Fig. 4. 2D-IR spectra of c-P6·T6+˙ (a) and l-P2+˙ (b) at 400 fs delay, with pump (FWHM ∼80 cm⁻¹) centered at 2080 cm⁻¹. Black solid and blue dashed contour lines correspond to positive (ESA) and negative (GSB) signals, respectively. Vertical dashed lines correspond to different experimental spectra, where probe a was changed to cover region 1300 cm⁻¹ to 1900 cm⁻¹ and probe b was centered in the 1900–2150 cm⁻¹ region for each experiment (see Fig. S14–S23† for time resolution of each probe window). Probe windows in 1300–1900 cm⁻¹ were stitched together by normalizing all probe a spectra to probe. b (c) fit of on-diagonal slice for l-P2+˙ (red line in (b)) using the sum of two Voigt. (d) The peak–peak distance for each time delay, calculated from the fit in (c).