Intensity-dependent control of dissociation pathways in strong-field double ionization of ethylene

We investigate the dissociation dynamics of ethylene (C2H4) in strong femtosecond laser fields using a reaction microscope. Coincidence iondetection enables reconstruction of fragment momenta and identification of multiple twobody channels of C2H2+4, including C2H+3 +H+, CH+2 +CH+2, and C2H+2 +H+2. Particular attention is given to the symmetric CH+2 +CH+2 channel. With increasing laser intensity, the kinetic energy release peakshifts from 5.2 eV to7.3 eV, indicating a transition from dissociation via lower excited states (e.g., 3B3u and 1Au (S2)) to higher-lying states(e.g., 3Ag and 1B3g). The observed evolution of state populations highlights that peak laser power density governs the selection of dissociation pathways. By tuning laser parameters, specific channels can be enhanced or suppressed, providing an effective approach for steering molecular fragmentation dynamics in polyatomic systems.