Knowledge Bank

Endothermic electron-transfer reactions of selected atomic negative ions $(D-$, $O-$, $S-$, $SH-$, $Cl-$, $Br-$, $I-)$ with various inorganic molecules have been investigated using a double mass spectrometer of in-line configuration. Plots of the charge-transfer cross sections as a function of translational energy yield energy thresholds which can be employed in conjunction with the known electron affinities of the atomic reactants to calculate molecular electron affinities. For some of these reactions, the thermal energy distribution of the neutral target leads to Doppler broadening of the cross-section curves in the threshold region, and errors form this source can substantially exceed those due to the kinetic energy spread in the incident ion beam. In such instances, the true thresholds have been determined by a fitting procedure which involves calculation of the effective energy distribution, and convolution of this distribution with an assumed threshold function, chosen on the basis of the best fit to the experimental results. Electron affinity data derived in these experiments will be reported for $O2$, NO, $NO2$, $SO2$, $CS2$, $Cl2$, $I2$, $Br2$, $SF6$ and several fluorocarbon molecules.