Natural widths in open-shell atoms: TheKabsorption spectrum of atomic oxygen

Total-ion-yield measurements and Hartree-Fock calculations are presented for the $1s\to \mathrm{np}$, $n=2\mathrm{} \mathrm{to} 5$ photoexcitations in atomic oxygen. Energies and relative intensities of the $\mathrm{}\left[1s\right]2s^{2}2p^4\left({}_{}{}^4{}_{}{}^{}P\right)np$ and $\mathrm{}\left[1s\right]2s^{2}2p^4\left({}_{}{}^2{}_{}{}^{}P\right)np$ series members are determined, and the apparent linewidths are measured. It is shown that natural widths in an open-shell atom can be deduced from an absorption spectrum only with the aid of theoretical input. The linewidth for the six individual components contained in the $1s\to 2p$ transition is determined to be 140(9) meV.