Knowledge Bank

We have used a time-of-flight method to measure the distribution in velocity and angle of the metastable molecules formed by electron bombardment of a collimated beam of thermal energy molecules. The velocity distributions show features, previously unreported but quite pronounced in hydrogen and helium, such as two distinct peaks whose positions and relative intensities depend strongly on the deflection angle and on the energy of the bombarding electrons. The considerations of scattering kinematics developed to explain these observations should facilitate the interpretation of experiments such as the spectroscopy of metastable $atoms1$ and $molecules,2$ time-of-flight studies of repulsive molecular $states,3$ and analyses of the kinetic properties of single-and multi-component $gases.4$