Production of Excited Atomic Hydrogen and Deuterium from $H_2 $ and $D_2 $ Photodissociation

We have measured the production of both $Ly\alpha $ and $H\alpha $ fluorescence from atomic H and D for the photodissociation of $H_2 $ and $D_2 $ by linearly-polarized photons with energies between 24 and 60 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. Our data are compared with \textit{ab initio} calculations of the dissociation process, in which both doubly-excited state production and prompt ionization through non-resonant channels are considered. Agreement between our experimental data and that of earlier work [1], and with our theoretical calculations, is qualitative at best. [1] E.Melero Garc\'{\i}a, J.\'{A}lvarez Ruiz, S.Menmuir, E.Rachlew, P.Erman, A.Kivim\"{a}ki, M.Glass-Maujean, R.Richter, and M.Coreno, J.Phys.B \textbf{39}, 205 (2006). Support provided by the NSF (Grant PHY-0354946), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme).