16 lines of the principal series of Cs(6 2 s 1/2 to 7-16 2 p 3/2 and 6 2 s 1/2 to 7-12 2 p 1/2 ) were investigated in absorption. Cesium vapour density was varied from 10 13 up to 10 17 cm -3 . Red asymmetries of all lines (extended red wings) were detected. This can be understood if electron transitions in the long-range interaction region follow the selection rules of molecules. It was established that the red and the blue wings of the lines each can be fitted to lorentzian profiles in small wavelength intervals. With the help of quasistatic theory the interaction constants from the long-range interaction potential Delta omega =C 3 /r 3 multiplied by the oscillator strength were determined from measurements. For all lines the ratio of C 3 (red)/C 3 (blue) was found to equal 2 in accordance with earlier theoretical calculations. In the far line wing, deviation from a lorentzian profile occurs. This was interpreted as a consequence of electron transition in the short-range region of interatomic potentials.
The atomic number densities of 87 Rb vapor and surrounding gas 3 He in a sealed cubic cell were measured by sweeping the absorption line and fitting the experimental data with a Lorentzian profile. The absorption was carried out around the D1 transition at different temperatures. We compare our results for the number density for 87 Rb with the previous methods and calculate the fractional error to be less than 5% as well as the error for 3 He between this work and the density obtained from the filling procedure to be no more than 4.2% at 370K. In addition, we discuss the factors that contribute to the error, among which the cell temperature plays the most important role.
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.
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 absorption spectra of pure Cs and Rb vapours and a mixture of both have been measured in the wavelength region from 2300 to 3100 AA (photoionisation continuum of the atoms) in the temperature range from 410 to 540 degrees C. Pronounced absorption bands can be detected in this wavelength region. Because the absorption was found to depend proportionally on the product of the number densities of the associated atoms (N Cs 2 , N Rb 2 and N Cs N Rb ) and the energies of many observed bands correspond roughly to the sum energies of two electronically excited species, the bands are interpreted in terms of simultaneous excitation of two atoms due to the absorption of one photon ('continuum-state absorption'). For the Cs-Cs and the Cs-Rb systems analogous bands were also observed within the discrete spectra of the atoms involved ('bound-state absorption'). Enhancement of the cross section for pair absorption near dipole-allowed transitions was found in agreement with theoretical predictions.
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.