H$\alpha $ Fluorescence Intensity and Polarization from Photodissociated H$_{2}$, D$_{2}$ and HD

We have measured the intensity and linear polarization of H$\alpha $ (n=3$\to $n=2) 656.3 nm fluorescence resulting from H and D atoms created by photodissociation of H$_{2}$, D$_{2}$ and HD using linearly-polarized photons with energies ranging from 16.5 to 17.6 eV. Between the threshold for atomic n=3 production at 16.6 eV and the n=4 production threshold at 17.3 eV, the relative cross section and polarization data are free from cascade contributions due to higher-lying atomic states. The photon beam energy width used for this work was 3 meV. Comparison of relative intensities to previous measurements [1] show marked differences. However, the polarization is in qualitative agreement. [1] H. Frohlich \textit{et al.}, Z. Phys. D \textbf{34}, 119 (1995). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme).