Rate of Recombination of Nitrogen Atoms

Abstract

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, $$\mathrm{N}+\mathrm{NO}\to {\mathrm{N}}_2+\mathrm{O}.$$ 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, $$\mathrm{N}+\mathrm{O}+\mathrm{M}\to {\mathrm{NO}}^{*}+\mathrm{M},$$ 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, $$\mathrm{N}+\mathrm{N}+\mathrm{M}\to {\mathrm{N}}_2+\mathrm{M},$$ was determined by this experimental method to be $${\text{k=1.72(±0.17)×10}}^{\text{−32}}{\mathrm{cm}}^6/{\mathrm{molecules}}^2\sec .$$ The third body was nitrogen or argon; the rate coefficient was the same for both gases within the limits of error given.