Velocity resolved REMPI spectroscopy: a new approach to the study of photodissociation dynamics

A new data acquisition mode has been implemented to a velocity-map ion-imaging setup, which records the velocity distributions of molecular photofragments with vibrational and rotational resolution. Compared to conventional velocity-map ion-imaging, the acquired data are of remarkable brilliance. This allows for unambiguous assignment of the fragment quantum states and the analysis of all rotational bands apparent in the electronic transition of the molecular fragment. The acquisition time is the same as required for recording a REMPI spectrum of the photofragments. The method is illustrated by the measurement of the rotational state distribution of NO created in the photolytical decomposition of NO2 at 225 nm. Different rotational distributions were observed for each vibrational state and for each of the four energetically accessible electronic channels.