The spectral lineshapes of the Sr (51P1–51P0) resonance transition perturbed by rare gases have been examined with a high-resolution laser-induced fluorescence method. In He and Ne, the collisional broadened spectral profiles are found to be symmetrical over the entire studied pressure range (0–600 Torr). The resulting line shapes are accurately represented by a simple Voigt profile expression. The Ar, Kr, and Xe perturbing gases, however, produce anomalous asymmetrical line broadening. To our knowledge, this represents the first measurement of asymmetrical broadening in the near wings of the emission profiles of the Sr-rare gas systems. Quantitative comparisons of the measured and theoretical line asymmetries suggest that atomic interactions in the Sr-rare gas systems are not entirely due to van der Waals (R-6)-type interactions. The line asymmetries could be caused by the correlations between thermal motions of the Sr atoms and collisional interactions.
We have measured Ar- and Kr-induced broadening of the Ca 4 s 2 1 S -4 s n p
1P(6⩽n⩽10) and 4 s 2 1 S -3 d 4 p 1 P transitions by means of the total absorption method. In this regime of n , the broadening cross section increases to its maximum value with n and then decreases. The maximum value is 28×10 -14 cm 2 at n =8 for Ar and 72×10 -14 cm 2 at n =9 for Kr. Assuming that the interatomic potential is described as a superposition of the Fermi potential and the polarization potential, we have calculated the cross section on the basis of the classical broadening theory. This calculation agrees well with both the present result and that for the Na 3 S - n S transitions measured by Kachru et al . by means of the trilevel-echo technique.
The cross sections for the collision-induced transfer of excitation from the
2P23 level to the
2P21 level of the first excited states of the alkali atoms have been measured for several alkali-noble gas systems. The cross sections were determined with a conventional resonance fluorescence technique in which the radiation from a spectral source was absorbed and re-emitted by an alkali vapor at low pressure (\ensuremath{\sim}${10}^{\ensuremath{-}6}$ Torr), and the scattered light analyzed with a scanning spectrometer. Provision was made for the introduction of various noble gases at controlled pressures into the alkali vapor. The determined cross sections are (in units of ${10}^{\ensuremath{-}16}$
cm2): Na-He, 41.1\ifmmode\pm\else\textpm\fi{}2.9; Na-Ne, 36.1\ifmmode\pm\else\textpm\fi{}2.5; Na-Ar, 64.6\ifmmode\pm\else\textpm\fi{}5.2; Na-Kr, 68.2\ifmmode\pm\else\textpm\fi{}5.5; Na-Xe, 61.8\ifmmode\pm\else\textpm\fi{}4.9; K-He, 52.8\ifmmode\pm\else\textpm\fi{}5.8; K-Ne, 14.0\ifmmode\pm\else\textpm\fi{}1.2; K-Ar, 34.0\ifmmode\pm\else\textpm\fi{}3.1. The quoted errors are estimated 70% confidence intervals. The measurements are compared with other experimental results and with various estimated cross sections.
We have made comprehensive measurements of the noble-gas-induced (He, Ne, Ar, Kr, and Xe) broadening cross sections of the Na $3S\ensuremath{-}nS$ ($3S\ensuremath{-}nD$) transitions, from
n=5to38 (
n=4to40). These measurements were made using the trilevel-echo technique and are an extension and refinement of our earlier work. We find that the cross sections increase as the geometric cross section at low values of
n, and then, at a value of
n which depends on the particular noble gas, begin to decrease and eventually reach an asymptotic value at high
n. The broadening cross sections for the nearly degenerate
D states are significantly larger than those for the
S states and clearly show the effect of
l-changing collisions. We also compare our measured
S-state broadening cross sections with the cross sections calculated using the theory of Omont and find good qualitative agreement.
Measurements of the collisional relaxation of the potassium resonance levels are reported. Effects due to the presence of nuclear spin are allowed for in the case of 2 P 1/2 and found to be negligible in the case of 2 P 3/2 . Reasonable overall agreement is found with calculated cross sections based on the Pascale and Vandeplanque potentials (1974). The natural lifetimes of the resonance levels are found to be tau ( 2 P 1/2 )=25.0+or-0.3 ns and tau ( 2 P 3/2 )=26.3+or-1.0 ns, and the sum of the resonance values is in good agreement with recent SCF calculations.