Femtosecond Nonadiabatic Confinement of Molecular Dication Yield

TL;DR

This study demonstrates that ultrafast nonadiabatic relaxation in molecular dications can confine their formation to a femtosecond timescale, revealing a new dynamic in strong-field ionization processes.

Contribution

The paper introduces a combined experimental and theoretical approach to observe and explain femtosecond-scale nonadiabatic confinement in molecular dication yields.

Findings

Peak dication yield at ~15 fs delay observed experimentally

Ab-initio calculations reproduce the delay and explain its origin

Nonadiabatic relaxation limits the ionization window to a few femtoseconds

Abstract

Doubly charged molecular cations often carry signatures of electronic correlation and electron-nuclear entanglement present in the parent cation. Here, we produce ethylene dications using a combination of an extreme ultraviolet pump and near-infrared probe pulses, observing a peak in the dication yield at a pump-probe delay of approximately 15 fs. Ab-initio calculations, which explicitly take into account coupled electron-nuclear dynamics induced by the pump and the multiphoton nature of the probe-induced ionization step, reproduced the observed delay in the yield. It originates from resonant enhancement of the multiphoton ionization of the electronically excited ethylene cation as the carbon-carbon double bond expands. However, this effect is tempered by rapid nonadiabatic relaxation of the excited ionic states. Our results suggest a general mechanism whereby ultrafast nonadiabatic relaxation of a molecular ion can compete with its strong-field ionization rate, confining the dication yield to a narrow temporal window of a few femtoseconds.