THEORETICAL ASPECTS OF THE UNIMOLECULAR DECOMPOSITION OF NITROUS OXIDE

Abstract

The kinetic data for the unimolecular decomposition of nitrous oxide, recently analyzed by Johnston, have been considered from the standpoint of the theories of unimolecular decompositions. Particular attention is paid to the high-pressure first-order rates, the low-pressure second-order rates, and the pressure range over which the rates fall off. A normal-mode analysis is made for the molecular vibrations, and calculations are made on the basis of N. B. Slater's theory. It is found that when the change of multiplicity is taken into account the Slater theory gives a satisfactory interpretation of the high-pressure behavior, but gives rates that are much too small in the low-pressure region. The theories of Hinshelwood, Kassel, and Rice and Ramsperger account more satisfactorily for the rate of activation, and Kassel's theory accounts for the pressure fall-off. A modified theory of unimolecular reactions is proposed to explain the observed results.