New studies on active nitrogen. I. Brightness of the after-glow under varied conditions of concentration and temperature

Abstract

This paper examines quantitatively the behaviour of nitrogen gas emitting the after-glow, under varied conditions. The integrated light emitted under the most favourable conditions has been measured as 3.18 candle-sec. per c.c. of nitrogen, the (rarefied) nitrogen being reckoned as at N.T.P. The number of quanta emitted is estimated as about 1.3 x 10-3of the number of molecules present. It is concluded, in agreement with Kneser, that the addition of unexcited nitrogen to glowing nitrogen increases the (instantaneous) emission. It was found that a fivefold increase of total pressure produced about a fivefold increase of brightness. These tests were carried out at very low luminous intensities, when the spontaneous decay was negligible during an experiment. If the active gas contained in 1 litre of weakly glowing nitrogen is allowed to diffuse quickly into an additional 1 litre volume of nitrogen, so as to dilute it by half, the candle power per unit volume is reduced about 4.3-fold. This is a fair approximation to the value 4, which would be expected if the reaction were bimolecular as regards active nitrogen, and is in agreement with the conclusion which has generally been drawn from observation on the rate of decay of the luminosity in closed vessels. The effect of compressing the glowing gas has been re-examined, using a solid piston moving in a cylinder. It is now found that with the improved arrangements the brightness varies as the inverse cube of the volume. This is the logical conclusion from, and confirmation of, the previous experiments in which the concentration of (1) the inert nitrogen, and (2) the active nitrogen, are separately varied. A further test was to expand the glowing gas into a doubled volume which was carried out by letting it pass into a supplementary exhausted vessel. This was expected from the previous result to reduce the intensity 8 times, but in fact did not reduce it more than 7 times. The gas was therefore somewhat brighter after the expansion than had been expected. Most sources of error would have the opposite effect, and there is an outstanding discrepancy in this result. The effect of temperature on the nitrogen after-glow is examined quantitatively, maintaining the cooler and hotter portion in pressure equilibrium. Cooling to liquid air temperature, for instance, increases the brightness some 80 times. Most, but not all, of this is due to the additional concentration. Assuming (in accordance with the compression experiment) that the brightness is as the cube of the concentration, and correcting the results to uniform concentration, it is found that over the range examined the brightness varies asT-0.64, whenTis the absolute temperature. The positive temperature effect on ordinary chemical reaction corresponds to something more likeT+100.