Probing H₂⁺ Formation in Strong-Field Ionization of Water Using Pump-Probe Spectroscopy and Covariance Mapping*

Understanding the ultrafast dynamics governing molecular fragmentation under intense laser fields is crucial for advancing strong-field physics and attosecond science. In this work, we investigate the formation of H₂⁺ from water (H₂O) during strong-field ionization using a femtosecond pump-probe technique combined with covariance mapping analysis. A near-infrared femtosecond laser pulse initiates ionization and dissociation, while a delayed probe pulse further ionizes the evolving molecular fragments. By employing covariance analysis of electron-ion momentum distributions, we resolve ionization pathways leading to H₂⁺ formation. Our results provide insights into the ultrafast proton migration and charge redistribution mechanisms that facilitate molecular hydrogen cation production.