Atomic Absorption Cross Section of Sodium Vapor Between 2400 and 1000 Å

The continuous atomic absorption cross section of sodium vapor has been measured using photoelectric techniques from the $3s{}_{}{}^2{}_{}{}^{}S\to \mathrm{np}{}_{}{}^2{}_{}{}^{}P_{}^0{}_{}{}^{}$ series limit at 2412.6 Å, down to 1000 Å. The bandwidth of the monochromator was 1 Å, and values of the cross section were obtained at about 2-Å intervals. The best value for the atomic absorption cross section at the series limit was 0.130±0.018 Mb. A zero minimum was observed at 1950 Å, in agreement with theoretical predictions but conflicting with previous experimental results. The reasons for this conflict are discussed, and a description is given of the experimental procedures adopted.