Throwing Light on Molecules Falling Apart: Photofragment Imaging

In this account, a method to visualise the breaking of chemical bonds—termed photofragment imaging—is reviewed. Photofragment imaging is a multiplex detection technique which enables one to determine in a single experiment the velocity as well as quantum-state distributions of products formed in a molecular dissociation. The correlated measurement of velocity and quantum-state distributions provides extremely valuable information beneficial to the investigation of chemical reaction dynamics. State-selectivity in the product detection is achieved using lasers and multiphoton ionisation techniques. Photofragment velocity distributions are obtained using two-dimensional time-of-flight methods. The emphasis in this account will be on unimolecular photodissociations of jet-cooled molecules, although more recently the technique has been extended to study bimolecular reactions as well. All the systems discussed are neutral molecules, but the photofragment imaging technique should be equally applicable to ionic systems.