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 ion detection enables reconstruction of fragment momenta and identification of multiple two-body channels of ${\mathrm{C}}_2{\mathrm{H}}_4^{2+}$, including ${\mathrm{C}}_2{\mathrm{H}}_3^{+}+{\mathrm{H}}^{+}$, ${\mathrm{CH}}_2^{+}+{\mathrm{CH}}_2^{+}$, and ${\mathrm{C}}_2{\mathrm{H}}_2^{+}+{\mathrm{H}}_2^{+}$. Particular attention is given to the symmetric ${\mathrm{CH}}_2^{+}+{\mathrm{CH}}_2^{+}$ channel. With increasing laser intensity, the kinetic energy release peak shifts from 5.2 eV to 7.3 eV, indicating a transition from dissociation via lower excited states (e.g., ³B_3u and ¹A_u (S₂)) to higher-lying states (e.g., ³Ag and ¹B_3g). 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.