Charles B. Leffert

Ionizing collisions of cesium with Cl2, Br2, and I2

A crossed molecular beam apparatus is used to study ionizing collisions of energetic cesium atoms with Cl2, Br2, and I2. The cross sections for formation of Cs+ are reported in the near−threshold region. The experiment combines an energy resolution better than 0.1 eV (FWHM) with a deconvolution procedure. An electron affinity of 2.50 eV is deduced for all three halogens, in good agreement with previous work. In a separate experiment, with cesium energies from threshold to 350 eV, and with much poorer energy resolution, the intensity ratios X−/X−2 are obtained. The results can be reasonably explained with an electron jump model. At energies below 30 eV, the observed ratios are in agreement with two other investigators, but between 150−350 eV they are drastically different from work reported from a third. Complementary data recently reported by a fourth group are difficult to reconcile with the present results.

Measurement of the electron affinity of NO2

The translational energy dependence of the relative cross section for Cs+NO2→Cs++NO2− has been measured in the threshold region using crossed molecular beams. Good energy resolution in the center of mass is obtained with a time‐of‐flight technique for the Cs primary beam and by numerical analysis of the remaining c.m. energy spread. The data are well represented by convoluting a c.m. cross section with the experimental energy spreads. This relative cross section has a threshold at 1.39±0.05 eV and yields an adiabatic electron affinity for NO2: 2.50±0.05 eV.

A Time‐of‐Flight Chemical Accelerator for Low Center‐of‐Mass Energy Spreads

An apparatus to obtain high resolution of relative kinetic energy for collision experiments in the electron volt range is described. Because it is the center‐of‐mass system that is important in the interpretation of experiments, energy spreads in both the projectiles and the targets are considered. We achieve high resolution in a primary beam with a time‐of‐flight technique. The target particles are in the form of a crossed beam. Basically, the scheme consists of observing only those reaction products that are formed in a short range of primary‐beam flight times. This means that good resolution may be obtained in spite of any inherent energy spread in the beam. The measured quantity is modeled mathematically to show the effect of the energy spreads that remain. These calculations may be used to arrive at the true velocity dependence of the center‐of‐mass cross sections.