Electronic and Nuclear Wavepacket Dynamics in Polyatomic Molecular Cations Probed by XUV Transient Absorption Spectroscopy

We report attosecond resolved transient absorption spectroscopy measurements of charge directed chemical reactivity in strong field ionized polyatomic molecules. An octave spanning mid infrared (MIR) pulse drives multiphoton ionization and launches coupled electronic and nuclear wavepackets in the molecular cation, which are probed by a broadband extreme-ultraviolet (XUV) supercontinuum spanning 40–72 eV. Time and energy resolved core to valence absorption features directly track ultrafast population flow and charge transfer dynamics across ionic channels. We have studied iodomethane (CH₃I) and iso-iodopropane (i-C₃H₇I) cations, revealing few femtosecond dynamics and clear signatures of charge transfer with a measurable lag between spectral bands, consistent with delayed population redistribution through intermediate states and autoionization mediated pathways. In parallel, we resolve coherent vibrational motion in the ionic manifold, providing a mode specific view of the evolving nuclear wavepacket and a basis for scaling studies with molecular size and bonding topology. We further outline a three-pulse strategy, adding a tunable (MIR–visible) control field to steer the nuclear wavepacket along competing field dressed potential energy surfaces.