Quenching of excited alkali atoms and related effects in flames: Part II. Measurements and discussion

Abstract

An alternating current photoelectric device has been used for determining the yield factor p of resonance flourescence of the yellow sodium doublet and the infrared and blue potassium doublets in flames at atmospheric pressure as a function of the temperature and composition of the burnt flame gases. From these measurements, the specific effective quenching cross section S (averaged over a Maxwellian velocity distribution) of the doublets considered for nitrogen, carbon dioxide, carbon monoxide, oxygen, hydrogen, argon, and water molecules could be derived. Remarkably, the S values for water molecules appeared to be very small compared to the values for the other diatomic and triatomic molecules. For nitrogen, carbon dioxide, hydrogen, and oxygen molecules, the specific effective quenching cross section appeared to be inversely proportional to the temperature in the range from 1700° to 2500°K. The S values found for the diatomic molecules H 2, N 2, and O 2 show a pronounced dependence on the resonance defect Δ E (that is, the difference between the alkali excitation energy and the nearest molecular vibrational energy). Large S values are associated with small energy defects. For a given † E value, however, the unsaturated diatomic carbon monoxide molecule shows a relatively large effective cross section, compared to the other diatomic molecules mentioned. Comparison of our S values with those reported in the literature yields further information about the dependence of S on the mean relative velocity of approach for sodium atoms in collision with nitrogen molecules. The effect of radiative nonequilibrium o on the intensity of the outgoing flame radiation, as calculated in Part I of this paper for a spectral line with Lorentz broadening, was investigated by means of line-reversal temperature measurements as a function of atomic density in the flame. Also, the effect of radiative nonequilibrium on the shape of the emission curve of growth, as predicted in Part I for flames with a high yield factor p, was studied in experiments with a hydrogen as predicted in Part I for flames with a high yield factor p, was studied in experiments with a hydrogen-oxygen-argon flame.