Catalyzed Recombination of Nitrogen Atoms, and the Possible Presence of a Second Active Speciesin Active Nitrogen

Abstract

The reactions of ethylene, ethane, and ammonia with active nitrogen have been studied over the pressure range 0.3 to 4 mm zlsi7zg a n z~nlteated reaction vessel. The object was to determine why each reactant shows, as is well-lanown, a smaller extent of reaction a t lower temperatures than would be predicted from the atorn concentration. It was concluded that ethylene probably brought about ltomoge~zeot~s cczlalyred recoii~hinalion, i.e. the process N + C2H4 + N.C?H.,, followed by N + N.C?I-I< + N? + C?Hr. The over-all third-order rate constant appeared to be very large, about 1.8X10-28 cc2 1nolec~1le-~ seccl. The behavior of ammonia was quite different from that of ethylene and it was, in fact, possible to show that the extent of reaction was not governed by the instantaneous atom concentration a t all. The results can be explained qualitatively, however, if it is assumed that excited ll~olecules formed in the course of homogeneous atom decay constitute a second active species in active nitrogen. This view serves also t o explain the failure in such work as that of Kistialcowsky et al. to observe ammonia destruction or escited molecules when especially low atom concentrations are used. The few esperime~lts involving ethane were sufficient to show that the reactivity was low for a different reason than with ethylene.I11 a previous study ( I ) , active nitrogen was produced in a condensed discharge a t pressures between 0.3 and 4 IIIIII and under conditions of approximately complete initial dissociation. I t was then allowed to flo~v rapidly through a "decay tube" to a reaction vessel, where the limiting (i.e. maximum) rate of I-ICS production from ethylene or ethane a t 350' C was assumed to measure the flowrate of residual N atoms. Informntion on the rate constants for N atom decay was thus obtained. The present experiments have been co~lducted along similar lines, the same apparatus being used; however, the L L a~t i v i t y " of the active nitrogen has been derived with the reaction vessel z~nlzeated. 11Ieasurements were made of I-ICN production from ethylene and ethane, and also of the decomposition of ammonia.Ethylene and ethane are of particular interest a t lower temperatures since they are typical of several substances with which the extents of reaction a t all temperatures approach well-defined limiti~lg values as the flowrate of reactant is increased, yet these values are significantly temperature dependent and, except a t the highest temperatures, are substantially less than might be expected from the available N atom concentration (2, 3, 1). An explanation for such behavior has been given by Forst et al. (A), who suggested that N atoll1 reactions might be accompru~iecl by extensive recombination of the atonls catalyzed by the reactant. (Such a process is not eliniinatecl by increasing the flo\vrate of reactant provided it is of the same order in reactant as the main reaction. On the other hand, ordinary homogeiieous and surface decal-, as well as recombination catalj-zed by a Prodzict, mould ...

Active Nitrogen.

“…in a coated reaction vessel, the active nitrogen pressure was found to be greater than the apparent atom concentration (87). The discrepancy was found to decrease as the K atom concentration approached zero.…”

The Reactions of Active Nitrogen With Boron Trichloride and Germane

“…The increase in the ratio of C12:BzC14 in the products is then readily explained if the BClz formed in [2] suffered extensive reaction with N atoms a t low flow rates of BC13, but dilnerized to a progressively larger extent as the flow rate of BC13 was increased. I t is interesting to note that, since the ground state of BN appears to be a triplet (21), the reaction BCI?…”

“…For example, the experimental data available a t present indicate that the maximum extent to which NH3 is decomposed by active nitrogen is only about one-sixth of the maximum extent to which HCN may be produced from hydrocarbons or hydrocarbon derivatives (1)(2)(3). This, in turn, is comparable with the iiiaximum extents to which active nitrogen reacts with 0 2 (4) and NO2 ( 5 ) , but is considerably less than the maximum extent to which it reacts with KO (5, 6).…”

EFFECT OF ADDED AMMONIA ON THE REACTIONS OF ACTIVE NITROGEN WITH CH4, C2H6, AND C2H4

“…'The s~nall increase in HCN procluction a t higher flow rates of the hydrocarbons might be due partly to reaction initiated by s~llall amounts of N2(.4) molecules formed by the recoinbination of N atollls in the presence of reactant (2), and partly to a slow direct reaction of N atoms with the hydrocarboi~. The much higher maximum HCN yield a t higher reaction temperat~~res (approximately equal to tliat Irom C2H., a t about 400" C in either a spherical or cylindrical vessel (9,4,5)) is allllost certainly clue to a much faster rate of the direct N-atonl attacl; under such conclitions.…”