Electron affinities from endothermic negative-ion charge-transfer reactions. III. NO, NO2, SO2, CS2, Cl2, Br2, I2, and C2H2

Translational energy thresholds have been measured for electron transfer reactions from various atomic negative ions to NO, NO2, SO2, CS2, Cl2, Br2, I2, and C2H2 using a tandem mass spectrometer. These thresholds, corrected where necessary for thermal broadening, were utilized with known thermodynamic data to calculate electron affinities for the molecules indicated. These results were also shown to be consistent with electron affinity limits established by observations of certain exothermic reactions of the molecular negative ions. The isotope distributions in the products from the reactions of monoisotopic Cl− and Br− with natural Cl2 and Br2, respectively, suggest that these reactions proceed via a linear X3− intermediate in which good ``mixing'' of the available energy occurs. The implications of this model with respect to the significance of the measured energy thresholds is discussed.