Collisions of atomic hydrogen with oxygen, sulfur, sodium and halogen anions at low energies

Total electron detachment and charge transfer cross sections, \sigma\sb{\rm e}(E) and \sigma\sb{\rm ct}(E), have been measured for collisions of the negative ions O\sp{-}, S\sp{-}, F\sp{-}, Cl\sp{-}, Br\sp{-}, I\sp{-}, Na\sp{-}, and K\sp{-} with atomic hydrogen for laboratory energies ranging from 2 to 500 eV. For the systems F\sp{-}, Cl\sp{-}, Br\sp{-}, O\sp{-} and S\sp{-} + H, \sigma\sb{\rm e}(E) displays no barrier for associative detachment; the results are found to be adequately described by simple curve-crossing models based upon available intermolecular potentials, or by classical orbiting models which assume that the anion interacts with the H atom via an attractive potential of the form 1/R\sp4. Analysis of \sigma\sb{\rm e}(E) for the system S\sp{-} + H required the cross section for \rm S\sp{-} + H\sb2\to e +\... to be experimentally determined, and these results resolved an apparent discrepancy in previous measurements. The measured detachment cross section for the Cl\sp{-}+ H is also found to be in agreement with a calculation for that system based on the effective range potential model. Unlike the other halogen anion-hydrogen systems, \sigma\sb{\rm e}(E) for I\sp{-} + H is found to increase with increasing energy over the higher collision energies investigated. The cross section for charge transfer in collisions of O\sp{-} S\sp{-}, F\sp{-}, Cl\sp{-}, Br\sp{-} and I\sp{-} with atomic hydrogen is found to be less than 1 A\sp2 over the entire range of laboratory energies investigated. A reasonable extrapolation of \sigma\sb{\rm ct}(E) for collisions of O\sp{-} + H is found to agree with a previous measurement at a higher collision energy. For the collision systems K\sp{-} and Na\sp{-} + H, \sigma\sb{\rm ct}(E) is found to be much smaller than \sigma\sb{\rm e}(E). The measured detachment cross section for Na\sp{-} + H is described using available potential energy curves and by assigning the anion state an average lifetime in the unstable region. A perturbed stationary state calculation of \sigma\sb{\rm ct}(E) for the reactant Na\sp{-} is performed, and this calculation underestimates the observed cross section for charge transfer at low collision energies

New Abundance Determinations of Cadmium, Lutetium, and Osmium in the r-process Enriched Star BD+173248

We report the detection of Cd I (Z = 48), Lu II (Z = 71), and Os II (Z = 76) in the metal-poor star BD+173248. These abundances are derived from an ultraviolet spectrum obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This is the first detection of these neutron-capture species in a metal-poor star enriched by the r-process. We supplement these measurements with new abundances of Mo I, Ru I, and Rh I derived from an optical spectrum obtained with the High Resolution Echelle Spectrograph on Keck. Combined with previous abundance derivations, 32 neutron-capture elements have been detected in BD+173248, the most complete neutron-capture abundance pattern in any metal-poor star to date. The light neutron-capture elements (38 <= Z <= 48) show a more pronounced even-odd effect than expected from current Solar system r-process abundance predictions. The age for BD+173248 derived from the Th II/Os II chronometer is in better agreement with the age derived from other chronometers than the age derived from Th II/Os I. New Hf II abundance derivations from transitions in the ultraviolet are lower than those derived from transitions in the optical, and the lower Hf abundance is in better agreement with the scaled Solar system r-process distribution.Comment: 6 pages, 4 figures. Accepted for publication in ApJ (Part 2)