Dissociative ionization of benzene in intense laser fields of picosecond duration

Mass spectrometry experiments have been performed to probe the morphology of dissociative ionization of a ring molecule benzene when it is immersed in a laser field of 35-ps duration whose intensity is in the range ${10}^{13}\hspace{0.5em}{\mathrm{W}\mathrm{}\mathrm{cm}}^{-2}.$ The field-induced fragmentation pattern is grossly different from that obtained by electron impact. The intense laser field clearly gives rise to much more fragmentation. Covariance mapping has been applied to study field-induced formation of highly charged molecular ions. Results indicate that the overall fragmentation dynamics is complex and is likely to involve both fast ladder switching as well as multiple ionization of fragment molecules at some intermediate steps in the ladder. Angular distributions of fragment ions have been measured. Anisotropic distributions indicate that some fragments are produced from precursors that are strongly aligned along the direction of the laser polarization vector while at least one fragment is formed from a precursor whose angular distribution is markedly isotropic. The nature of the precursors remains to be discovered.