Fig. 3

Fourth-order rephasing 1Q–0Q–1Q 3D spectrum of TIPS–TAP²⁻ in THF. a Experimental and c simulated rephasing 1Q–0Q–1Q 3D spectra, shown in absolute values. The energies of the main absorption band at 2.06 eV and the progression band at 2.23 eV are indicated as dashed black lines in the ∆ℏω_T = 0 plane as a guide for the eye. Red and blue dashed vertical lines mark positive and negative shifts of 0.17 eV, respectively, along the 0Q axis ∆ℏω_T. Isosurfaces are drawn at 2.3, 9.0, and 35% of the maximal signal amplitude. Contour lines of the 2D projections of the spectral solids are drawn at linearly spaced levels of the normalized signal amplitude with an additional contour line at 0.05. The spectral volumes inside the red and blue cuboids, which are centered around peaks A and B are isolated and shown on the right. There, isosurfaces are drawn at 50, 70, and 90% of the isolated maximal signal amplitudes whereas the color bars indicate the signal levels (normalized to the highest absolute value of the respective full 3D spectrum) for each contour line. b Double-sided Feynman diagrams that describe the peaks A (red) and B (blue)