Pressure Effects of Foreign Gases on the SodiumD-Lines

Abstract

The effects of foreign gases (A, ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$) on the $D$-lines of Na have been studied by means of a steel absorption chamber, in which the Na-vapor pressure is kept low while the foreign gas pressure varies between 0 and 17 atmospheres. Temperatures were such that true line contours could be photographed and photometrically evaluated. Results are: (1) The red shift of the absorption maximum varies linearly with the density of the perturbing gas. (2) Study of the line contours reveals marked asymmetries, most pronounced near the base. Asymmetries are to the red in case of A and ${\mathrm{N}}_2$, slightly to the blue for ${\mathrm{H}}_2$. (3) Both $D$-lines show the same broadening and shift. (4) The effects can be accounted for theoretically by assuming a distance of closest approach between excited Na and the foreign gas molecules of about 9A. Quantitative results are summarized in Table I.