Photoinduced Dynamics of Carbonyl Compounds: Direct Visualization of Diradical Intermediates by Ultrafast X-ray Transient Absorption Spectroscopy
Final Report Abstract
In summary, in this work we report the Mn L-edge soft X-ray spectra of solid-state MnIII(acac)3 at low temperatures of 30 K and 80 K, along with the room temperature spectra. At low temperatures, we immediately notice the MnII signal which results from X-ray induced damage. However, the contribution of the damage does not increase with the increasing number of scans at the same spot, which we cannot fully explain at present. We speculate two possible reasons behind this phenomenon: 1) reduced diffusion of secondary radicals and subsequent recombination at low temperatures; 2) reduced diffusion of the chain propagation reaction. We see a slight increase in X-ray induced damage by increasing the temperature from 30 K to 80 K. At room temperature, we see a gradual increase in damage signal with increasing number of scans (passes) due to the accumulation of radiation dose. Using the dose limit and other experimental parameters discussed here, we validate other experimental approaches, such as, fs pulses from XFELs, which provide faster accumulation of signal compared to diffusion-driven damage and fast-flowing liquid jets at synchrotron sources. In addition, increasing the sample surface area and reducing dwell time on each spot will substantially reduce the accumulated dose and thus the radical induced photoreduction. These approaches may enable measurements of damage free soft X-ray spectra of model and actual metallo-organic/inorganic compounds and protein complexes.
