Since the onset of the 3.5 Å signature is earlier than the 1.4 Å and 2.4 Å signatures, it cannot be related to the increase of the R1 and R2 distances of αTp at early times. Comparison with transient ∆PDF signatures based on AIMS simulations, which are in quantitative agreement with the experimental results (see Fig. ), suggests that it is connected to a reduction in the distances between the methyl ring substituent and a few of the ring carbons. The evolution of the mean of one of such distances is plotted in Fig. , blue, together with the R1 (yellow) and R2 (red) distances. It shows a reduction towards 3.5 Å before the onset of the increases in the R1 and R2 distances. The origin of such a distance decrease can, for geometric reasons, only be a bending motion of the methyl substituent out of the plane of the conjugated π-system of αTp.