The Reactive Components in Active Nitrogen and the Role of Spin Conservation in Active Nitrogen Reactions

Abstract

Critical examination of the available experimental information provides rather convincing evidence that atomic nitrogen is the main reactive species in active nitrogen. I t appears quite unlikely that a significant contribution to the activity is made by electronically excited molecules, metastable atoms, ions, or triatomic radicals. Evidence exists, however, for the presence of more than one active species, and a plausible suggestion would seem to be that the second species is vibrationally excited molecules. Consideration of the role of spin conservation in reactions of active nitrogen leads to the conclusion that reactions that conserve spin occur more readily than those in which spin is not conserved. INTRODUCTIONA proposed unified interpretation (15) of the many reactions of active nitrogen that have now been studied made it essential to define as clearly as -possible the nature of the reactive species in active nitrogen formed in a con--densed electrical discharge. Numerous investigations into the properties of active nitrogen have been made and explanations of its behavior have been suggested from time to time. However, there is no recent critical evalu a t' ion which seeks to correlate all the results. Such an evaluatioil seems possible, and is attempted in the present paper, now that the dissociatioil energy of the nitrogen molecule has been established with virtual certainty. T H E REACTIVE COMPONENTS O F ACTIVE NITROGENAtoms and molecules in almost every conceivable excited state have been suggested as possible active species in active nitrogen. I t is now widely accepted that the activity is due mainly, though perhaps not entirely, to atomic nitrogen (8, 12, 33, 45,52, 56). Electronically Excited Molecules and Atoms a s Active SpeciesT h e A32 state should be the longest lived electrollically excited state of molecular i~i t r o g e n .~ During the emission of the Lewis-Rayleigh afterglow of active nitrogen the A 3 2 state is colltinually being formed in small amounts because it is the lower state of the electronic transition B311 + A 3 2 that gives the afterglow (Fig. 14). I t has a lifetime with respect to radiation of to 10-hec. (47) and must have a still shorter lifetime with respect to collisions to explain the absence of Vegard-Kaplan bands in the emission spectrum of 'iVlanuscript received Marclz 28, 1956. Contribzltio?~ from the Physical Chemistry Laboratory, iWcGil1 University, Montreal, Quebec, withfLna?tczal For personal use only. 1218CANADIAN JOURNAL OF CHEMISTRY. VOL. 34. 1956 the afterglow. In the conventional fast flow systems used to study the chemical reactions of active nitrogen (e.g. 14), a lifetime of about sec. for electronically excited nitrogen molecules formed in the discharge tube would mean that their concentration would be reduced by a factor of about lo9 by the time they reached the reaction vessel. Since collisioils will reduce the lifetime considerably below sec., it seems quite certaiil that electronically excited nitrogen molecules formed in the discharg...

Silent Discharge Reactions in Aqueous Solutions. V. Nitrogen Fixation in a Heterogeneous System of Nitrogen and Water

“…Besides the aforementioned nitrogen atoms and molecular ions, metastable atoms or molecules may also play some role as active nitrogen. 23,24) The formation of active nitrogen in the atmosphere should be also expected in the present work. Though it is very important to clarify the state of active species, this study is concerned only with reactivity.…”

The Reactions of Active Nitrogen With Cyclopropane, Cyclobutane, and Cyclopentane

“…As in previous papers, it will be assumed that atomic nitrogen is the main chemically reactive species in active nitrogel1 (9).…”

The Kinetics of the Decay of Nitrogen Atoms as Determined From Chemical Measurements of Atom Concentrations as a Function of Pressure

“…On the other hand, the production of HCN from ethylene under conditions of complete consumption ("cleanup") of active nitrogen (high ethylene flowrates and elevated temperatures), a mode of measurement frequently used in past work (e.g. 17, IS), would likely reflect the atom concentration alone owing to the high activation energy to be expected in most reactions involving excited nitrogen molecules (13).3 HCN production also has the advantages that it is not subject to mechanical failure and, since negligibly small quantities of other nitrogencontaining compounds are formed (20,21), it provides an absolute value of the atom concentration. Production of HCN from ethylene was therefore chosen to measure the N atom concentration and the results were checked using ethane.…”

“…Accordingly, the time of decay was much shortened and the data should have indicated more directly the variation of [NIo. However, a cleanup of N atoms was difficult to achieve, so that the clestruction of ammonia, which is apparently due to excited molecules present in the active nitrogen in small amounts (12,13,16) For personal use only. and capacitance are given in Fig.…”