Ionization and fragmentation dynamics of molecules at high x-ray intensity

Ludger Inhester, Kota Hanasaki, Oriol Vendrell, Sang-Kil Son, and Robin Santra

[BibTeX]http://www.dpg-verhandlungen.de/year/2016/conference/hannover/part/a/session/39/contribution/7

X-ray free-electron lasers (XFELs) provide ultraintense and ultrashort x-ray pulses, which can sequentially ionize molecular samples many times. A molecule that is charged up by these many ionizations will dissociate rapidly into highly charged ion fragments. We have developed an ab-initio electronic structure toolkit, XMOLECULE [1], to describe coupled ionization and fragmentation dynamics induced by intense XFEL pulses. In this approach we solve rate equations for the electronic state populations using a kinetic Monte Carlo scheme while the nuclei are propagated classically. For all the visited electronic states transitions rates and forces on the nuclei are calculated on the fly based on the Hartree-Fock-Slater model. Our calculations show that charge rearrangement effects play an important role for the ion yield distribution. Remarkably, we also find that the total charge yield of a molecule is enhanced compared to the sum of charge yield of its constituent isolated atoms. These findings are supported by recent experiments with methyl iodide (CH₃I) at LCLS. [1] Struct. Dyn. 2, 041707 (2015).

Tags: H2O, x-ray multiphoton ionization, XMOLECULE, XFEL, CFEL, DESY