Pressure Effects of Homogeneous Rubidium Vapor on Its Resonance Lines

The broadening of the resonance lines of rubidium in absorption under pressures up to 150 mm of its own homogeneous vapor was studied by means of a 21-foot grating. Under pressures below 1 mm the broadening of the lines was very symmetrical and the line contours could be described by the dispersion formula, but when the pressure was high the lines exhibited asymmetrical broadening of van der Waals type. The ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ component showed red, while the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ component showed violet asymmetry. Both lines showed the proportionality of the width with $N$, the concentration of Rb atoms. The experimental width at half-maximum is greater than that predicted by Houston's theory by a factor of 1.5 and the width of the transition from ${}_{}{}^3{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ is greater than that from ${}_{}{}^3{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ by a factor of 1.6. A narrow diffuse band was observed near the shorter wave-length side of the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ component and a similar one near the longer wave-length side of the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ component.