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

Abstract

Absolute total cross sections for electron detachment and H-(D-) production have been measured for collisions of 0-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 Hformation via the ion-molecule reaction 0-+ H2 ---+ H-+ OH, whereas a barrier of about 1 eV is observed for H-production in collisions ofS-with H 2 ·

Electron detachment and charge transfer for collisions ofO−andS−<

“…(5) and the results of Ref. [10] for o(Hz, e). For E (1 eV, however, a different method must be employed because the present experiment extends to energies below those for S +Hz given in Ref.…”

“…A There are two motivations for measuring electron production cross sections for S +H2. First, the analysis of the data for S +H requires a knowledge of the cross section for the molecular target for collision energies below those given by Huq et al [10]. Second, it is not readily apparent that the results of Ref.…”

“…The determination of the absolute cross sections for producing free electrons [i.e., reactions (1) and (2)] and charge transfer is accomplished by normalization to those cross sections previously measured for 0 +Hz [10]. For a given laboratory energy e, the cross section for the atomic target for either channel is given by…”

“…For E (1 eV, however, a different method must be employed because the present experiment extends to energies below those for S +Hz given in Ref. [10]. Consequently, we must determine o (Hz, e) independently for E (1 eV in the following manner: a beam of Cl is made simultaneously with S such that one can switch between S and Cl taking data for both systems at a given laboratory energy.…”

“…The cross section for 0 +H~H + is known [10]; for example, it is about 2.3 A for an 0 energy of 12 eV. For 0 +H, this laboratory energy (12 eV) corresponds to a relative collision energy of 0.7 eV, which is below the energetic threshold for charge transfer.…”