Production of Excited Atomic Hydrogen and Deuterium from H$_{2}$, D$_{2}$ and HD Photodissociation

We have measured the production of Ly$\alpha $ and H$\alpha $ fluorescence from atomic H and D resulting from the photodissociation of H$_{2}$, D$_{2}$ and HD by linearly-polarized photons with energies between 20 and 65 eV. In this energy range, excited photofragments result primarily from the production of doubly-excited molecular species which promptly autoionize or dissociate into two neutrals. Comparison between the relative cross sections of H$_{2}$ and D$_{2}$ and the available theory show only qualitative agreement. We will discuss the various systematic effects which affect this and other types of synchrotron-based measurements in this energy range. Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme).