Alexie Boyer | Searcharxiv

arXiv2026

Femtosecond Nonadiabatic Confinement of Molecular Dication Yield

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.

physics.chem-ph↗

arXiv2025

Ultrafast probing of isotope-induced explciit symmetry breaking in ethylene

Symmetry governs nature's law, yet many of the natural phenomena occur due to the breakdown of symmetry. Here, we show how isotope-induced inversion symmetry breaking influences ultrafast photoisomerization processes in ethylene. Using extreme ultraviolet pump-near infrared probe time-of-flight mass spectrometry, we find that replacing one of the carbon atoms in ethylene with a 13C isotope leads to twice-faster structural relaxation via ethylene-ethylidene isomerization in the photo-excited molecular cation. Advanced trajectory surface hopping calculations incorporating the nuclear symmetry of the molecular systems, reveal that it arises from the mixing of different normal modes in the isotope-substituted species, interactions otherwise forbidden by symmetry. Although the mixing does not alter the symmetry of the electronic Hamiltonian, it modifies that of the nuclear Hamiltonian, causing explicit symmetry breaking. This facilitates efficient intra-molecular vibrational energy redistribution, lowering the isomerization yield. Our findings offer opportunities to use isotope-induced nuclear symmetry breaking to control the outcome of light-molecule interactions across ultrafast timescales.

physics.chem-ph↗