This dissertation divides naturally into two parts: one concerned with processes taking place in the gas phase and the other with research involving processes taking place on surfaces. Both make use of the measurement of the velocity and angular distributions of product molecules to provide clues and understanding of how chemical processes occur on the molecular level.

I start with presenting work on gas phase chlorine isocyanate (ClNCO) photodissociation utilizing photofragmentation translational spectroscopy to measure the velocity distributions of photodissociation products, under collision-free conditions using synchrotron radiation as UV ionization source. The distributions of the fragments from the primary photodissociation pathway reflect the formation of linear isocyanate radical (NCO) and another high-energy form of NCO which, however, needs to be identified through future work. The measurements also provide a new experimental value for the heat of formation of ClNCO that is significantly different from the previously accepted value. High level electronic structure calculations are in good agreement with our new value for the heat of formation.

In the second part of the thesis, I describe the development of a new technique for surface research based on a technique that has been used very successfully in the gas phase chemical dynamics research: velocity map imaging (VMI). Our new instrument yields three-dimensional velocity distributions of reaction products desorbing from a solid surface. We have applied this instrument to study atoms desorbed from a KBr single crystal surface. Even for this extensively studied model system, our measurements revealed new information about the photodesorption dynamics. The most interesting of these results is tantalizing preliminary evidence for a preference for ejection of Br along directions connected to the structure of the sample. This kind of information would be almost impossible to obtain using conventional techniques for measuring velocity distributions. The results show the unique capability of the VMI technique and the great promise it has of contributing to a new level of understanding of chemical processes occurring on surfaces.