Lifetime, Coherence Narrowing, and Hyperfine Structure of the(6s26p7s) P1∘3State in Lead

The lifetime and hyperfine structure of the $\left(6\mathrm{}{s}^{2}6p7s\right) {}_{}{}^3{}_{}{}^{}{P}_1_{}^{\circ }{}_{}{}^{}$ excited state in lead have been investigated by the technique of level-crossing spectroscopy. The lifetime of the state was determined to be $\tau =5.75\mathrm{}\left(20\right)\mathrm{}\times {10}^{-9\mathrm{}}$ 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 $f\left(3639\mathrm{} \mathrm{\AA }\right):f\left(4058\mathrm{} \mathrm{\AA }\right)$ oscillator-strength ratio measured by Khokhlov, one may infer the absolute $f$ values: $f\left(2833\mathrm{} \mathrm{\AA }\right)=0.169\mathrm{}\left(17\right)\mathrm{}$, $f\left(3639\mathrm{} \mathrm{\AA }\right)=0.040\mathrm{}\left(8\right)\mathrm{}$, $f\left(4058\mathrm{} \mathrm{\AA }\right)=0.155\mathrm{}\left(31\right)\mathrm{}$. The high-field level crossing in the hyperfine structure of the first ${}_{}{}^3{}_{}{}^{}{P}_1_{}^{\circ }{}_{}{}^{}$ state of ${\mathrm{Pb}}^{207}$ was found to occur at a magnetic field $H_c=4661.1\mathrm{}\left(4\right)\mathrm{}$ G, which corresponds to a magnetic-dipole-interaction constant $A=8.811\mathrm{}\left(17\right)\mathrm{}\times {10}^9$ cps.