Abstract
We present studies on intra-molecular charge redistribution in iodine containing molecules upon iodine-4d photoionization. For this, we employed an XUV-pump-XUV-probe scheme based on time-delayed femtosecond pulses delivered by the free-electron laser at DESY in Hamburg (FLASH). The experimental results show delay dependent and molecule-specific iodine charge state distributions that arise upon multiple iodine-4d photoionization. Using the example of CH3I and CH2I2, we compare the delay-dependent yields of I3+. We model the involved processes using advanced ab initio electronic structure calculations which include electron correlations combined with a classical model of the nuclear motion. The qualitative agreement of our model with the experimental results allows us to relate the observed, strongly molecule-specific efficiencies of the intra-molecular charge rearrangement not only to molecule-specific fragmentation timescales but also to molecule-specific electronic structure and molecular environment.
Highlights
Charge rearrangement between atomic centers is vital for the formation and breaking of chemical bonds in molecules
The time resolved XUV-pump XUVprobe studies have been performed at 82.7 eV photon energy with average pulse energies of 40 μJ and a focal spot size of about 50 μm using the split-and-delay unit (SDU) of the PG2 beamline, which is based on the grazing incidence Mach-Zehner geometry [10]
The FEL pulse duration was in the range of 80 fs ± 30 fs for the CH3I and 100 fs ± 30 fs for the CH2I2, which has been estimated by measuring the electron bunch length by the LOLA setup [11]
Summary
Charge rearrangement between atomic centers is vital for the formation and breaking of chemical bonds in molecules. Assuming a negligible efficiency for I3+ resulting from single photoionization followed by a cascade of Auger decays, the almost complete charge redistribution in CH2I2 prevents the occurrence of the I3+ ions in two subsequent photoionization processes.
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