Broadening, Asymmetry and Shift of Rubidium Resonance Lines under Different Pressures of Helium and Argon up to 100 Atmospheres

A new absorption tube was constructed which made feasible the study of the pressure effects of foreign gases on the absorption lines of alkali vapors of homogeneous density and temperature. In addition to helium and argon at pressures up to 100 atmospheres, hydrogen was used up to 20 atmospheres. Up to relative density 46 the broadening is proportional to the concentration of helium or argon gas. The slopes of the half-width vs. relative density curves are 0.735 ${\mathrm{cm}}^{-1\mathrm{}}$ and 0.594 ${\mathrm{cm}}^{-1\mathrm{}}$ per unit relative density of helium for ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ components, respectively, and the corresponding values for argon are 0.855 ${\mathrm{cm}}^{-1\mathrm{}}$ and 0.627 ${\mathrm{cm}}^{-1\mathrm{}}$ per unit relative density. Helium produces a violet, argon a red asymmetry. The degree of asymmetry increases as the concentration of foreign gas increases, and is comparatively much greater for argon. For argon the asymmetry of the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ component is greater than that of the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ component, while for helium the reverse is true. Argon produces a greater shift than helium. The former produces a strong red shift, the latter a violet shift. For both gases the shift of the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ component is greater than that of the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ component. For helium the shift appears to be proportional to the relative density, and the shift of the longer wave-length component is about twice as great as that of the shorter wave-length component, while for argon the shifts for the doublet components are quite close, and the relation between shifts and relative densities obeys in general the 3/2 power relationship. Optical collision diameters as calculated from the half-width data are 13.37A and 7.753A for Rb—A and Rb—He, respectively. From the measurements of the amount of total absorption from the line contours, $f$ values and the transition probabilities were evaluated.