## Dissertations, Theses, and Masters Projects

1994

Dissertation

#### Degree Name

Doctor of Philosophy (Ph.D.)

Physics

#### Abstract

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.

#### DOI

https://dx.doi.org/doi:10.21220/s2-4rdj-pq48