Normalized plot of the fraction of unconverted SeMet (red error bars) against the X-ray fluence experienced by the sample at 12680 eV (droplet 38 from Table 1). The dose absorbed by the sample is indicated on the top x-axis and the fluence delivered is on the bottom x-axis. The blue solid line is the best-fit exponential curve to the data. The dotted brown line represents the fraction of selenium atoms in the sample that have experienced one or more direct collisions with an X-ray photon (photoionization events). Here we use a photoionization cross section of 157 cm2 g−1 for Se at 12680 eV (Hubbell, 1982). Clearly, the change in the XANES spectrum is too fast to be a direct result of primary photoionization of SeMet by X-ray photons. The breakdown of the Se—C bond must be the result of secondary or tertiary events.