Oscillator Strengths of Ca II, Sr II, and Ba II

The lifetimes of the $5p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and $5p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ states of ${\mathrm{Sr}}^{+}$ and the $6p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and $6p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ states of ${\mathrm{Ba}}^{+}$ have been measured by the Hanle-effect technique with optical excitation from the ion ground state. (The lifetimes of the ${\mathrm{Mg}}^{+}$ $3p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${\mathrm{Ca}}^{+}$ $4p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ states were obtained by the same technique and reported previously.) These ${\mathrm{Ca}}^{+}$, ${\mathrm{Sr}}^{+}$, and ${\mathrm{Ba}}^{+}$ states each decay to a ${}_{}{}^2{}_{}{}^{}D_{\frac{3}{2},\frac{5}{2}}^{}{}_{}{}^{}$ doublet as well as to the ground ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ state, and the branching ratios for these transitions have been measured. The ions were produced by introducing traces of the atomic vapor into an argon discharge. Consequently, the cross sections for collisional depolarization of these ${}_{}{}^2{}_{}{}^{}P_J^{}{}_{}{}^{}$ states due to collisions with argon were also obtained from the measurements. The experimental results are given in Tables I and II. A discussion of the ion-atom collisional depolarization cross sections is included.