Thermal dissociation and recombination of hydrogen according to the reactions H2+H⇄ H+H+H

Abstract

Three‐body recombination and dissociation rate coefficients (kr and kd , respectively) for the reactions H 2 + H ⇄ H + H + H have been evaluated for temperatures ranging between 300 and 10 000°K on the basis of the modified phase‐space theory of reaction rates and Monte Carlo trajectory calculations. The semiempirical Porter‐Karplus surface for H3 was used in the calculations. Good agreement was obtained between the theoretical estimates of kd and the bulk of the dissociation rate measurements. However, in contradistinction to some of the recent experimental investigations, neither the extremely steep temperature decay ([inverted lazy s] T −6 ) of kr at high temperatures nor the existence of a pronounced maximum in kr at moderate temperatures are supported by this theoretical work. Possible reasons for these differences are suggested. A simple ratio was deduced which relates k r ( H ) and the corresponding rate coefficients of the isotopes of hydrogen. The result is in good agreement with available experimental measurements and enables one to predict the latter rate coefficients without additional trajectory calculations. An example is given to illustrate the capability of the present Monte Carlo method in obtaining other useful information about atomic and molecular collision processes.