Theory of vibrational relaxation in mixtures of ortho- and para-hydrogen

Abstract

A numerical study of the vibrational relaxation at 500 K of a mixture of ortho-H, and para-H, is described. The required state-to-state rate constants were calculated from the quantum results of Rabitz and co-workers, and missing pieces of data were estimated by interpolation.It is concluded that only one relaxation time will be observed in any mixture of ortho-H, and para-H, and that (except at very high dilutions in a third inert gas) the relaxation rate constant will be close to the mean of the individual rate constants for relaxation, weighted according to the respective mole fractions of ortho-Hz and para-H, present in the mixture.We find that the relaxation process can be modelled very accurately as an electrical RC network, whose time constants can be written down quite easily as sums of the appropriate microscopic rate constants, and by using this model, it is a simple matter to explore the conditions required for a mixture of two gases to exhibit two distinct vibrational relaxation times. On conclut qu'un seul temps de relaxation pourra btre observe pour tous les melanges de H, ortho et para et que (B ['exception des cas de tres fortes dilutions dans un troisieme gaz inerte), la constante de vitesse de relaxation sera voisine de la moyenne des constantes individuelles des vitesses de relaxation ponderees selon les fractions molaires respectives de Hz ortho et para presentes dans le melange. [Traduit par le journal]

Internal energy randomisation in weak-collision unimolecular reaction systems

“…[12] and [13]. The new rate constants agree with the old ones to better than 4 decimal places over the whole range of pressures, so that our earlier conclusions remain unchanged.…”