Imaging studies of photochemistry of the stratospheric bromine and chlorine compounds

This dissertation focuses on the photodissociation dynamics of stratospheric bromine and chlorine radical intermediates (BrO, ClO) along with reservoir species (ClONO2), which are known to play an important role at stratospheric ozone depletion. The experiments were carried out using a newly built velocity-map ion imaging apparatus which is an improvement over traditional translational spectroscopy studying photodissociation dynamics. The apparatus combines a collision-free molecular beam source with a laser-based pump-probe technique; i.e., single state pumping followed by a state-selective resonantly enhanced multiphoton ionization. Intense molecular beams were prepared using a custom-built flash pyrolytic source. The current research involves the development of fundamental properties of target species such as bond enthalpies and heats of formation, the chemical identification of photofragments, and their relative branching ratios, the excited states dynamics that lead to final products, partitioning of the available energy and finally the wavelength dependence of all these properties.