Recombination Of Nitrogen Atoms Research Articles

Recombination of Hydrogen, Nitrogen and Oxygen Atoms on Copper and Silver Single Crystal Surfaces

Abstract Recombination of hydrogen atoms, nitrogen atoms and oxygen atoms was carried out on single crystal surfaces of copper and silver subjected to various surface pre-treatments. With both the recombination of hydrogen atoms and that of nitrogen atoms, copper surfaces electrolytically polished have always higher activity than those chemically polished. The Cu(100) surface chemically etched by ammonium persulfate was more active than that etched by nitric acid for both hydrogen atoms and nitrogen atoms, whereas with the Cu(110) the opposite order of activity was obtained. For both silver and copper, no evidence was found to show the different order of activity between the recombination of hydrogen atoms and that of nitrogen atoms. Concerning the recombination of oxygen atoms on single crystal surfaces of silver, the (110) face was found to be more active than the (100) face in accord with the result of our earlier work about the recombination of hydrogen atoms on single crystal surfaces of copper.

Kinetics of Nitrogen Atom Recombination

The rate of recombination of nitrogen atoms in the nitrogen afterglow has been measured in a flow system using NO as a titrant and determining the NO content continuously by mass spectrometer. Above about 3 mm of mercury the reaction is predominantly homogeneous and third order. The rate constant, 5.7×1015 cc2 mole—2 sec—1, is independent of temperature in the interval studied (195–450°K). The rate is reduced by substituting helium or argon for N2 as the third body, the ratios of the third-order rate constants with these third bodies being about the same as those for recombination of iodine and bromine atoms. Below about 3 mm of mercury a pseudo-first-order wall recombination becomes important. The recombination coefficient was found to be 1.6×10—5 on a glass wall that undoubtedly was partly poisoned by water.

THE REACTION OF ACTIVE NITROGEN WITH HYDROGEN BROMIDE

The reaction of active nitrogen with hydrogen bromide was found to produce bromine and ammonium bromide as the main products, along with traces of compounds tentatively identified as bromamine, NH2Br, and bromimine, NHBr2. Hydrogen abstraction from hydrogen bromide by nitrogen atoms, imine and amine radicals can account for ammonia formation. Considerable catalysis of nitrogen atom recombination by hydrogen bromide appears to occur. A resonance transfer of the electronic energy responsible for the nitrogen afterglow to bromine with a resultant bromine emission spectrum is proposed to account for the orange reaction flame.

遊離酸素原子および窒素原子再結合反応に対する遷移金属の触媒能の比較

遊離酸素原子および窒素原子再結合反応に対する遷移金属の触媒能の比較

Thermometric Study of the Frozen Products from the Nitrogen Microwave Discharge

Thermometric observations have been made of the phenomena accompanying the stabilization and the recombination of free nitrogen atoms in a solid molecular nitrogen matrix at liquid helium temperatures. Condensation from the gas phase may occur at temperatures considerably above the 4.2°K coolant temperature as the result of the normal change in heat content and the heat of atom recombination. Estimates, made from the latter effects, of the free atom concentration in the gas phase were as high as 4 atom %. Qualitative confirmation of the presence of an energetic species stabilized in the solid phase was made by detection of heat release upon warmup. From the latter effect a minimum nitrogen atom concentration in the solid of 0.03 atom % was estimated. For the conditions used the initiation of atom recombination occurs at a temperature of about 9°K. The upper limit of about 36°K for stabilization coincides with the known thermal transition in solid nitrogen. The data suggest that at least above 9°K diffusion of nitrogen atoms occurs throughout the solid matrix during deposition from the gas phase. If recombination during warmup is diffusion-controlled, unusual dependence upon temperature is indicated.

Rate of Recombination of Nitrogen Atoms

The rate of recombination of nitrogen atoms by three-body collision has been determined at room temperature and 0.5–1.3 mm pressure. The nitrogen was dissociated (about 3–6% nitrogen atoms) in a condensed discharge and pumped continuously through a glass tube 4.2 cm i.d. and 2.5 m long. The atom concentration was measured at a given point by ``titrating'' the N atoms with NO which was introduced into the gas stream at this point which was a short distance from the discharge tube. The N atoms react essentially instantaneously with NO in this titration, N+NO→N2+O.When excess NO is added, the unconsumed NO combines with the O atoms formed yielding the typical oxygen afterglow. If insufficient NO is added, however, the unconsumed nitrogen atoms react with the O atoms formed, yielding the typical blue color of the NO bands, N+O+M→NO*+M,When the quantity of NO added essentially equals that of the N atoms, the gas is practically colorless. This gives the N atom concentration at this point. In order to determine the rate of recombination of the N atoms, the relative decrease in intensity of the yellow nitrogen afterglow was obtained by following the reaction along the tube by means of a photomultiplier. The intensity of the afterglow is known to be proportional to the square of the N atom concentration. With the decrease of N atoms as a function of time and with the absolute N atom concentration known at a given point, the rate coefficient could be determined. The over-all value of the rate coefficient for the recombination reaction, N+N+M→N2+M,was determined by this experimental method to be k=1.72(±0.17)×10−32cm6/molecules2sec. The third body was nitrogen or argon; the rate coefficient was the same for both gases within the limits of error given.

The Nature of Active Nitrogen

It is shown that the first bimolecular process found exprimentally in the decay of the nitrogen afterglow requires oxygen as a catalyst and draws both active bodies from a common population. An activation energy of 900 cm-1 is necessary for this afterglow process. The second bimolecular process involves two active bodies possessing monomolecular decays and drawn from different populations. Negligible activation energy is required for this afterglow process. This process is quenched by oxygen and requires a minute impurity believed to be hydrogen. The final monomolecular decay shows the usual diffusion-collision pressure dependence at higher temperatures and effectively diffusion dependence only at lower temperatures. The effects of diffusion are much reduced by a monomolecular layer of oxygen on the walls. An aggregate possessing a dissociation energy of 5600 cm-1 is involved in the final afterglow process. Reasons are given for believing that the first bimolecular process is recombination of nitrogen atoms in the presence of an oxygen molecular catalyst of the order of a few parts per million and that the second process is a collision of two different vibrationally excited ground states of the nitrogen molecule with a molecular hydrogen catalyst of the order of a few parts per million.

THE REACTION OF ACTIVE NITROGEN WITH HYDROGEN CHLORIDE

Hydrogen chloride was apparently destroyed by catalyzing the recombination of nitrogen atoms, the maximum observed rate of destruction being less than one sixth of the active nitrogen flow rate. The effects on the hydrogen chloride – active nitrogen reaction of added chlorine and added hydrogen indicated the reaction between hydrogen atoms and molecular chlorine to be the most important secondary reaction.

The Nitrogen Afterglow

THE phenomena connected with active nitrogen and its afterglow have recently received a great deal of attention. A view almost generally accepted now is that the afterglow is due to the recombination of nitrogen atoms produced in the discharge. Though it has not been possible hitherto to determine thermochemically the heat of dissociation of molecular nitrogen, a value a little above the equivalent of 11 volts has been found for it from the characteristics of its band spectrum. On the recombination of two atoms taking place to form a molecule this amount of energy may be transferred to a second molecule, and it is just sufficient to excite the afterglow bands. This view, it may be stated, is based on the assumption that the initial states giving rise to the first positive group of bands are the same as the final states involved in the production of the second and fourth positive group. The vibrational levels seem to be identical; the rotational levels have not yet been analysed.