M. S. Huq

Total electron detachment cross sections for collisions of H- and He and F- with atomic and molecular targets

Absolute total electron detachment cross sections for collisions of H- and D- with He, and F- with He, Ne, Ar, CO, N2 O2 and CO2 have been measured in the energy range from about 1 up to 300 eV. The results for H-(D-)+He are found to be in very good agreement with the recent theoretical calculations of Gauyacq (1980) and Taylor and Delos (1982). The thresholds for electron detachment in F- collisions are found to be approximately 7 eV for all targets except O2, which has a threshold of about 4 eV. For this latter case, evidence of some charge transfer producing O2- (or O-+O) is also observed.

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.

Reactive scattering and electron detachment in collisions of halogen negative ions with isotopic hydrogen molecules

Total cross sections for reactive scattering and collisional electron detachment have been measured for collisions of F− and Cl− with H2, D2, and HD. The collision energy extends from below the energetic thresholds for the processes studied up to a laboratory energy of about 300 eV. Reactive scattering is found to be the dominant inelastic channel for the case of the F− projectile. Isotope effects are observed in all cross sections. Electron detachment of F− is found to occur by two distinct mechanisms. A striking difference in the reactive and detachment cross sections is observed when Cl− is substituted for F− in that the electron detachment cross section is generally larger than that for reactive scattering. As in the F− case, isotope effects are also present for the Cl− projectile. The isotope effects observed for electron detachment of Cl− suggest that detachment cannot be described by any unique mechanism.

An ion beam study of reactive scattering of halide ions by methyl halides

Measurements of electron detachment cross sections, reactive charge transfer, and differential elastic and inelastic scattering cross sections for Cl−, Br−, and I− ions on CH3I, CH3Br, and CH3Cl targets are reported. The energy range for the experiments is from 3 to 150 eV. Of the very large number of reaction channels open, it appears that most make significant contributions to the total cross section for sufficiently high projectile energies. The SN2 reaction, which may be dominant at lower energies, was not observed and is probably not significant above the lowest energies in this study. Surviving primary ions exhibit a broad spectrum of inelastic loss, suggesting target breakup.

Measurements of absolute total cross sections for charge transfer and electron detachment of halide ions on chlorine

Absolute total cross section measurements are reported for electron detachment and for reactive scattering between the halide ions (Cl−, Br−, and I−) and chlorine gas Cl2. The charge transfer and dissociative charge transfer cross sections are found to be very large at their maxima, which occur at a relative collision energy of about 13 eV. The electron detachment cross section for I−+Cl2 is anomalously low. Some energy loss spectra are reported for I−+Cl2. They exhibit substantial inelastic scattering which is consistent with the calculated potentials of Cl2.

Reactive scattering and electron detachment for collisions of halogen negative ions with HCl, DCl, and HBr

Absolute total cross sections have been measured for collisions of Cl−, Br−, and I− with HCl, DCl, and HBr for projectile energies ranging from 5 to 300 eV. The processes investigated include reactive scattering and electron detachment. The reactive scattering cross sections exhibit considerable isotope effects and the collisional dynamics are discussed within the framework of a spectator‐stripping model which involves proton or deuteron abstraction. The results for the I− projectile are substantially different from those for Cl− and Br−; this difference is suggested to be related to the relative stability of the molecular anion, HI−.

Collisions of Cs- with atoms and molecules

Presents the results for measurements of the absolute total cross sections for electron detachment sigma e(E) and charge transfer sigma i(E) in low-energy collisions of Cs- with He, Ne, Ar, Kr, Xe, D2, N2, O2, CO, CO2, SO2, N2O, CH4 and SF6. In the case of the rare gases, the apparent energetic threshold for detachment is rather high (near E=50 eV); a similar observation has also been made for the Na- and K- projectiles. As before, a curve-crossing model well describes the observed sigma e(E). Structure in sigma e(E) for the CO2 target has been attributed to charge transfer to a metastable state of CO2-(2A1). Similarly, in the case of N2O, both sigma e(E) and sigma i(E) exhibit behaviour which suggests that charge transfer to a temporary negative-ion state of that molecule is involved in the collisional dynamics. Charge transfer is also observed to be an important exit channel for other molecules; for example, the value of sigma i(E=30 eV) is about 500 a02 for the SF6 target.