The hyperfine structure and lifetime of the 6 2 D 3/2 and 6 2 D 5/2 states in 39 K are studied experimentally. The states were excited from the ground state by two-photon absorption of the laser light pulses. The hyperfine-structure intervals, and hence the hyperfine-structure interaction constants, were obtained from the numerical analysis of the zero-field quantum beat signals. The unmodulated component of the fluorescence decay curve served to determine the lifetime. In a separate experiment a magnetic field was applied to induce partial decoupling of the electronic and nuclear angular momenta in the 6 2 D states. The sign of the magnetic dipole interaction constants was deduced from the resulting difference between the intensities of sigma + and sigma - polarised fluorescence.
The lifetime and hyperfine structure of the $(6{s}^{2}6p7s) ^{3}{P}_{1}^{\ensuremath{\circ}}$ excited state in lead have been investigated by the technique of level-crossing spectroscopy. The lifetime of the state was determined to be $\ensuremath{\tau}=5.75(20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec. The linewidth of the level-crossing signal was observed to saturate at a "coherence-narrowed" value in agreement with theoretical predictions. The magnitude of this narrowing corresponds to a 27(3)% branching ratio to the ground state. When the branching ratio and the lifetime are combined with the
f(3639A˚):f(4058A˚) oscillator-strength ratio measured by Khokhlov, one may infer the absolute
f values:
f(2833A˚)=0.169(17),
f(3639A˚)=0.040(8),
f(4058A˚)=0.155(31). The high-field level crossing in the hyperfine structure of the first $^{3}{P}_{1}^{\ensuremath{\circ}}$ state of
Pb207 was found to occur at a magnetic field
Hc=4661.1(4) G, which corresponds to a magnetic-dipole-interaction constant $A=8.811(17)\ifmmode\times\else\texttimes\fi{}{10}^{9}$ cps.
Measurements have been made of time-resolved fluorescence from n 2 S 1/2 and n 2 D 3/2 states of 133 Cs (n=8 to 14) over a range of vapour densities covering the onset of collisional depopulation. Lifetimes for the free atom and depopulation cross sections are deduced. Lifetimes are proportional to (n*) x with x=2.52+or-0.06 (S states) and 2.62+or-0.06 (D 3/2 states). Cross sections are proportional to (n*) 4 . Hyperfine-structure interaction constants for the 2 D 3/2 states determined by the method of quantum beats agree with the recent results of Belin et al. (1976).