Molecular Beam Study of the Hydrogen Iodide Reaction

Abstract

The results of experiments to determine reaction cross sections for the formation of HD in energetic collisions of HI with DI are reported. Molecular beams of HI, accelerated to energies of 40–215 kcal/mole by expansion from nozzles in mixtures with hydrogen or helium, were passed through a reaction chamber containing DI at low density. A mass‐spectrometer monitoring the gases effusing from the chamber was used to detect the HD reaction product. In the range of collision energies investigated, at approximately one‐half to two and one‐half times the activation energy of 44 kcal/mole, no HD attributable to reaction was detected. With HD formation assumed to be that corresponding to the lower limit of detection, the upper limit to reaction cross section is determined to be 0.04 Ų. Comparison is made with several models for reaction with differing energy requirements. The results indicate that rotational or vibrational excitation of colliding partners is required for an appreciable probability of reaction upon collision.