The authors have measured the absorption efficient in the quasi-static wings of the first potassium resonance lines in various K-Cs mixtures. At sufficiently high concentrations of caesium atoms both components of the potassium first resonance doublet have extended blue wings of the van der Waals type. The corresponding effective C 6 constants determined from the experimental data are (1.5+or-0.3)*10 -29 s -1 cm 6 and (2.4+or-0.5)*10 -29 s -1 cm 6 for the stronger and weaker components, respectively. The calculated values of the effective C 6 constants are 1.78*10 -29 s -1 cm 6 for the stronger component and 2.35*10 -29 s -1 cm 6 for the weaker component.
The broadening of the Na resonance lines, due to collisions with Rb and with Cs, has been measured with the use of the normalized fluorescence-intensity method of Chatham, Lewis, and Gallagher. Several Na resonance-radiation diffusion and absorption corrections were necessary in the Rb case, due to an unavoidable excess of Na density in the Rb vapor. The line-broadening rate coefficients
k1 and
k2 for the
D1 and
D2 resonance lines are ${k}_{1}(\mathrm{Rb})=(6.2\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$
cm3 ${\mathrm{s}}^{\ensuremath{-}1}$, ${k}_{2}(\mathrm{Rb})=(5.5\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$
cm3 ${\mathrm{s}}^{\ensuremath{-}1}$, ${k}_{1}(\mathrm{Cs})=(6.9\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$
cm3 ${\mathrm{s}}^{\ensuremath{-}1}$, and ${k}_{2}(\mathrm{Cs})=(5.5\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$
cm3 ${\mathrm{s}}^{\ensuremath{-}1}$ at $T\ensuremath{\simeq}300$\ifmmode^\circ\else\textdegree\fi{} C. The leading (${C}_{6}{R}^{\ensuremath{-}6}$) dipole-dipole long-range dispersion forces for the Na-Rb and Na-Cs interactions are calculated, and are used in the impact-theory formula to obtain theoretical line-broadening rate coefficients. These are in poor agreement with the measurements, indicating that as suggested by Vadla, the higher-order (${C}_{8}{R}^{\ensuremath{-}8}$) dispersion terms are also important at the very long range responsible for this line broadening.
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
2P21 component showed red, while the
2P23 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
3P23 is greater than that from
3P21 by a factor of 1.6. A narrow diffuse band was observed near the shorter wave-length side of the
2P21 component and a similar one near the longer wave-length side of the
2P23 component.
In addition to previous absorption measurements of Cs resonance lines, new investigations on Na, K and Rb also showed definitely that beyond symmetrical Lorentzian central parts of the lines, the stronger components of the resonance lines have blue and the weaker components red asymmetry. This behaviour can be explained by a quasistatic treatment of the self-broadening mechanism taking interatomic interaction potentials into account. But with additional data it is now possible to give a different interpretation of the origin of observed asymmetries than suggested in the previous paper on Cs resonance lines (see abstr. A5740 of 1975). The asymmetries are shown to arise from the mutual repulsion of two potential curves of the same species.