Quantum Molecular Charge-Transfer Model for Multi-step Auger-Meitner Decay Cascade Dynamics*

This work provides a quantum molecular description for modelling charge transfer dynamics during the structural damage of molecules following X-ray interactions. The absorption of X-ray's creates unstable core-hole states, which can decay via multiple autoionization steps in heavy elements. This leads to highly charged cations that undergo Coulomb explosion. The structural rearrangements following the decay of core-hole states have far reaching implications, new highly targeted cancer therapies are being developed that exploit Auger-Meitner decay cascades initiated by radionuclides bonded to small carrier molecules. There is hence a demand for simulations that can explicitly track both the ejection of electrons and the associated structural dynamics. Synchrotron experiments performing x-ray/ion coincidence spectroscopy can detect the charge states and kinetic energies of the various decay channels following the x-ray induced molecular break-up. These experiments provide reliable benchmarks for our novel quantum molecular dynamics method, which uses a time dependent set of trajectories to adiabatically simulate the population transfer across potential energy surfaces of increasing charge states. We use our model to examine the molecular bonding effects on the charge-transfer dynamics during the molecular breakup dynamics of IBr over multiple Auger-Meitner decay steps. We compare our new methods results with atomistic simulations combining Monte- Carlo/Molecular-Dynamics (MC/MD) simulations with a classical over-the-barrier (COB) model to track inner-shell cascades and redistribution of electrons. Our theoretical simulations are then compared against experimental coincident fluorescence/ion data.