The dissertation consists of two parts, where part I deals with the realization of the OH+D2 reaction and part II with the dissociation dynamics of iodine molecule above the first ionization limit.

Part I deals with the realization of the OH+D2 to HOD+D reaction. The main issue was to build a source of OH radicals with a sufficient high kinetic energy to overcome the barrier to the reaction of 5.3 kcal/mol. The OH radicals were produced by photolysis of a suitable precursor. Within this work, the OH radicals from two different precursors, H2O2 and HNO3, were studied concerning their rotational and thus their kinetic energy distribution. Also the total amount of OH radicals were compared, regarding the different precursors and also different molecular beam set-ups.

Part II deals with the photodissociation dynamics of the iodine molecule at excitation energies (10.2-20.4eV) above the first ionization threshold (9.31eV). This processes were studied with velocity map imaging, a special form of ion imaging. An analysis of the measured images showed that a variety of different processes were involved, among them production of free ion pair states, neutral dissociation of the iodine molecule and dissociation to a neutral iodine atom and an iodine ion via direct ionization to a repulsive ionic molecular state. A new process was found at excitation energies around 14eV which was attributed to a three-body-process, where the electron can take away a variable amount of kinetic energy, resulting in a very broad kinetic energy distribution of the I and I+ fragments. Coupling of a molecular Rydberg state which converges to a higher lying repulsive state of the iodine ionic molecule to a lower lying repulsive ionic molecular state is supposed to be the key mechanism.

Also a photoelectron spectrum was measured.