Precision Lifetime Measurements onNaI3p2P1/2and3p2P3/2by Beam-Gas-Laser Spectroscopy

The lifetimes of the fine-structure levels $3p{}_{}{}^2{}_{}{}^{}P_{1/2}^{}{}_{}{}^{}$ and $3p{}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$ in neutral sodium were determined at improved precision ( $\pm 0.13\%$, $1\sigma$) by means of the beam-gas-laser spectroscopy method. The resulting lifetimes of 16.299(21) and 16.254(22) ns, respectively, are in excellent agreement with the results of the most refined theoretical calculations. The long-standing discrepancy between ab initio line strength calculations and the measurements of Gaupp et al. [Phys. Rev. A 26, 3351 (1982)] for the $\mathrm{NaI}3s-3p$ transition appears to be resolved now. In addition, the hyperfine constants of the $3p{}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$ level were determined.