Quantum mechanical model of ultrafast disruptive probing for simultaneous tracking of multiple reaction pathways

Disruptive probing is an ultrafast pump-probe method in which a delayed pulse perturbs an evolving ionic species and modifies its subsequent branching among fragmentation pathways, allowing many dissociative channels to be monitored simultaneously through mass-resolved product yields. Here we present a reduced quantum-mechanical model that connects this experimental observable to coherent wavepacket dynamics on coupled ionic potential-energy surfaces. The model describes ionizing excitation as the preparation of a non-stationary parent-ion wavepacket, field-free evolution as coherent propagation with localized transfer into dissociative channels, and the delayed disruptive probe as a geometry-dependent perturbation that redirects final product branching. Complex absorbing potentials are used to convert outgoing dissociative flux into asymptotic yields, while dephasing, instrument-response convolution, and momentum ensemble averaging represent experimental broadening. The calculated signals reproduce the central qualitative features of disruptive probing, including channel-specific enhancements and depletions, decay of probe sensitivity as fragmentation proceeds, recurrence structure associated with parent-ion wavepacket motion, and smoothing of coherent features by ensemble averaging. Although formulated here for ionizing excitation followed by mass-resolved ion detection, the framework is general to delayed-perturbation measurements of channel-specific product observables and may be extended to multimodal measurements that combine ionic and neutral detection.