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.
Profiles of the singly ionized strontium resonance line at 421.6 nm (4p
2P1/2--4s
2S1/2) which are collisionally broadened by argon have been measured from the line core to near-wing region (within the distance of \ensuremath{\Delta}\ensuremath{\nu}\ensuremath{\lesssim}50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ from the line center). The observed broadening rate of the core is (1.87\ifmmode\pm\else\textpm\fi{}0.25)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at 690 K. A clearly asymmetric profile has been observed in the wing region. These results are discussed by considering semiclassical impact and quasistatic theories combined with theoretical interaction potentials for the
Sr+-Ar pair which were previously reported by the present authors.
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 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.