A novel experiment for near-threshold photodissociation studies is presented. State-selective excitation of the molecular photofragments to high-n Rydberg states is used in a variation of the ion imaging technique, allowing for undistorted detection of slow fragments produced close to the channel dissociation threshold. As a first demonstration of this method, the angular anisotropy parameter beta for production of NO (J=17/2) and O P-3(2) in the photodissociation of NO2 has been obtained as a function of excess energy. A classical model for beta as a function of excess energy is presented, accounting for the decrease of anisotropy in the angular photofragment distribution upon approaching the channel threshold. The experimental values of beta fluctuate substantially around the values predicted by the model, indicating strong underlying fluctuations in the state-to-state rate constant. This experiment offers in principle a unique route to measuring state-to-state reaction rate constants in situations where existing time- or frequency-resolved methods are inappropriate. (C) 2000 American Institute of Physics. [S0021-9606(00)01908-5].