The determination of cross sections for the quenching of resonance radiation of metal atoms I. Experimental method and results for sodium

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Abstract
A method of determining the cross sections for the quenching of excited metal atoms by molecules and atoms which may be present in flames is described. The method has been applied to the quenching of sodium atoms in the 3p2P state and the following results (in Å2) for the square of the distance between the centres of colliding species, σ2, obtained: σ2H2 = 2.87 ± 0.1; σ2N2 = 6.95 ± 0.15; σ2CO = 11.9 ± 0.4; σ2CO2 = 17.0 ± 0.4; σ2H2O = 0.5 ± 0.3; σ2O2 = 12.3 ± 0.5; σ2Ar < 0.1; σ2He < 0.1. These cross sections have been measured at temperatures in the range 1400°K to about 1800°K and found to be independent of the temperature. The values for the cross sections are derived from measurements of the fluorescence of sodium in hydrogen-oxygen flame diluted with various other gases. This method is believed to be free of uncertainties due to self-absorption, compound formation, line broadening effects and uncertain velocity distributions. Where values for cross sections have been obtained by other workers they are compared with these results and possible reasons for the discrepancies are discussed.

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