To assess the timescales of the wave-mixing decays, the emission signals are integrated over a narrow energy window corresponding to the Henning sharp states and fit to a convolution of the instrumental response and an exponential decay using a least squares algorithm (Fig. ). The application of this fitting procedure to three different datasets (Supplementary Section III) yields decays of 33 ± 6 fs, 53 ± 2 fs, and 94 ± 2 fs for the features emitting from the n = 5, n = 6, and n = 7 members of the Henning sharp series, respectively. Integrating over smaller angular regions of Fig. does not change the extracted decays appreciably. As expected, these time constants reflect the proportional increase in autoionizing state lifetime with (n*) 3 . However, these measured decays are not consistent with the calculated lifetimes of Henning sharp series, which will be shown in Section IIIC to decay on timescales nearly an order of magnitude longer than observed here. The decay of the wave-mixing emission instead corresponds to lifetimes of Henning diffuse series, as discussed further in the following sections.