The Absolute Rates of Reaction of Hydrogen with the Halogens

Abstract

In this paper we apply the statistical-mechanical method which has only recently been developed for reaction rates to three new groups of reactions. These are the reactions of I2, Cl and Br with the various kinds of hydrogen molecules. In the first type (I2+H2→2HI) symmetry properties enable one to divide the six internal modes of vibrations for the four coplanar atoms into three sets with one, two and three modes of vibration in each so that in obtaining the frequency nothing greater than a cubic is solved. This treatment of the frequencies will apply to a very broad class of reactions. The potential surfaces probably yield too high a zero-point energy for the activated state. In spite of this result they give the right relative rates for the various isotopic reactions because mass enters very strongly into what in the past has been thought of as the collision factor. The study of isotopic reactions in conjunction with the new theory of rates gives a detailed knowledge of the potential in the activated state and can be carried much farther than has been done in this preliminary treatment. The treatment has been carried far enough however to show its general applicability to these types of processes.