Multi-electron interaction control in molecules using ultrashort laser pulses

While electron-electron interactions play a fundamental role in any atom beyond hydrogen, they also govern molecular structure and reactivity. We introduce and experimentally demonstrate a general concept to control multi-electron interaction by intense, ultrashort laser fields. In particular, strong coupling to excited states allows to modify the effective exchange energy by infrared (IR) induced valence orbital mixing. For a proof-of-principle, we focus on the sulfur hexafluoride molecule, SF₆, considering the coupling of a sulfur 2p core hole with a valence excited electron on the few-femtosecond timescale, using a combination of soft x-ray and IR laser pulses. The IR laser intensity represents a control knob to tune the effective exchange interaction energy, resulting in a characteristic change in the spin-orbit-split oscillator strength ratio that is directly quantified in the x-ray absorption spectroscopy experiment. This is conducted on a purely electronic level without depending on nuclear motion or significant population transfer. Besides describing the underlying physics with a mechanistic fit model, these findings are validated by an ab-initio quantum-mechanical many-body simulation. Such direct control of effective electronic interactions and correlation is a significant step towards laser-directed chemistry on the fundamental electronic level with single-atomic site selectivity.