H$\alpha $, H$\beta $, and Ly$\alpha $ fluorescence from the photodissociation of H$_{2 }$and D$_{2}$

We have measured the intensity, corrected for polarization, of H$\alpha $ (656 nm), H$\beta $ (486 nm), and Ly$\alpha $ (122 nm) fluorescence from the photodissociation of H$_{2}$ and D$_{2 }$by linearly-polarized photons with energies between 25 and 150 eV. We observe a low-energy maximum in the intensities for all three transitions between 35 and 40 eV, due to excitation of doubly-excited molecular states. A second shoulder or secondary maximum is attributed to the direct production of excited $H_2^+ $ states which subsequently dissociate into the excited atoms. This second maximum is in qualitative agreement with the H$\alpha $ results of Garcia \textit{et al.} [1]. The effects of cascading and the size of the visible collision volume on these data is discussed. [1] Garcia \textit{et al.}, J. Phys. B \textbf{39, }205 (2006).