Ab initio study of highly charged ion-induced Coulomb explosion imaging

Abstract

We present a theoretical investigation of ion-induced Coulomb explosion imaging (CEI) of pyridazine molecules driven by energetic C$^{5+}$ projectiles, using time-dependent density-functional theory (TDDFT) with Ehrenfest nuclear dynamics. By systematically varying the projectile's impact point and orientation relative to the molecular plane, we compare orthogonal and in-plane trajectories and quantify their effects on fragment momenta, electron-density response, and atom-resolved ionization. Newton plots and time-resolved density snapshots show that trajectories avoiding direct atomic collisions yield the most faithful structural reconstructions, whereas direct impacts impart large, highly localized momenta that distort the recovered geometry. Planar trajectories generate substantially greater ionization and broader momentum distributions than orthogonal ones due to deeper traversal through the molecular electron cloud. Quantitative analysis of electron removal at 10~fs confirms that projectile proximity and orientation strongly modulate both local and global ionization. These findings clarify how impact geometry governs the fidelity of ion-induced CEI structural recovery and help explain the variability and noise observed in experimental CEI measurements. More broadly, the results highlight both the strengths and the intrinsic limitations of ion-induced CEI and identify key considerations for interpreting experiments.