Pathway-resolved photoelectron emission in dissociative ionization of molecules

Electron-ion coincidence detection allows one to visualize the ultrafast chemical reactions of molecules in strong laser fields. Here, by measuring the photoelectron angular distribution (PAD) of H-2 in strong laser fields correlated to different pathways, i.e., direct ionization when the internuclear distance is small, or ionization after the molecular bond stretches to a large internuclear distance, we uncover the roles of the molecular orientation and internuclear distance in the dissociative ionization of H-2. As compared to the first dissociation pathway, the regular nodal structures on the concentric above-threshold ionization circles vanish for the second pathway, which are numerically validated by the quantum simulations. Pathway-resolved PADs assisted by electron-ion coincidence detection open new possibilities to probe the rich dynamics of molecules in strong laser fields, in particular to image the instantaneous geometry of molecules. (C) 2016 Optical Society of America