Total cross sections for collisions of O- and S- with hydrogen

Absolute total cross sections for electron detachment and H- (D-) production have been measured for collisions of O- and S- with H2 and D2 for relative collision energies ranging from approximately 0.5 to 25 eV. Electron detachment appears to occur via several mechanisms. Isotope effects are observed in all cross sections. Threshold studies indicate that there is no appreciable potential barrier to H- formation via the ion--molecule reaction O-+H2 → H-+OH, whereas a barrier of about 1 eV is observed for H- production in collisions of S- with H2