A standard velocity map imaging (VMI) spectrometer makes use of three electrodes and produces VMI focussing conditions over a region of space only one to two mm in diameter. This is more than acceptable for a standard gas phase photodissociation (the archetypal VMI experiment) since all of the products are produced and ionised within the region defined by the intersection of a laser beam with a molecular beam, typically one mm or so wide.However, the great benefit of VMI (its excellent velocity resolution) cannot reliably be obtained in other reaction dynamics studies, such as those involving surface desorptions, since the product fragments are scattered into, and typically ionised over, a much larger region of space than that in which the VMI conditions exist.This thesis outlines the first systematic study of the relationship between "weak extraction" and the area over which VMI focussing conditions remain valid, and shows that, by making use of weak extraction, the VMI focussing conditions produced by our apparatus prevail over an area ∼12 mm in diameter.A new VMI spectrometer has been constructed and used to study the near threshold photodissociation of chloroform. The potential to use the apparatus for surface VMI studies was then investigated. This document contains an overview of gas phase photodissociation processes and the development of the VMI technique, followed by a detailed description of the newly constructed apparatus. A study of the photodissociation of chloroform (CHCl3 ) in the gasphase, and experiments and simulations which were carried out in order to determine the feasibility of adapting the spectrometer for surfaces are discussed. Finally, a description of the necessary modifications which were made to the apparatus in order to enable surface experiments is provided.