Coulomb imaging of the concerted and stepwise break up processes of OCS ions in intense femtosecond laser radiation

We study the break up of OCS in intense femtosecond laser radiation using the FEMPULS technique to vary the laser pulse duration from 7 fs to 200 fs. Newton and Dalitz plots show the progression of molecular deformation and break up for OCS³⁺ and OCS⁴⁺. For increasing pulse length, the concerted three body dissociation exhibits increasing bending, and the amount of stepwise dissociation decreases. For the longest pulses however the stepwise process increases again. Both phenomena can be interpreted in terms of the effect of the laser field on lower charge states and the behaviour of a wave packet on a saddle point potential. The experiment illustrates the ability of the Coulomb imaging method to track molecular geometry and dynamics and indicates a new path to laser control of molecular parameters.