Electron detachment in low-energy collisions of halogen anions with atomic hydrogen

Total electron-detachment cross sections σₑ for collisions of F^-, Cl^-, Br^-, and I^- with atomic hydrogen have been measured for relative collision energies E ranging from 0.1 to 20 eV. For F^-, Cl^-, and Br^-, σₑ is found to decrease with increasing E and is fairly well described by a simple orbiting model in which an effective polarizability is used to describe the interaction of the anion with atomic hydrogen at small internuclear separations. For the system I^-+H, σₑ increases with increasing collision energy. The measured σₑ for Cl^-+H is also found to agree well with calculations based on an effective-range approximation. Charge-transfer cross sections have been measured for F^-, Cl^-, and I^-+H and are found to be small.