Hyperfine Structure ofRb85,87in the5PState

The atomic beam resonance method has been used to investigate the hyperfine structure of the $5P$ excited states of ${\mathrm{Rb}}^{85}$ and ${\mathrm{Rb}}^{87}$. The apparatus and method of observation were similar to those in a previous experiment on the $3P$ state of sodium. For ${\mathrm{Rb}}^{85}$ in the $5P_{\frac{3}{2}}$ state, the magnetic dipole and electric quadrupole interaction constants are, respectively, $a_{\frac{3}{2}}=25.3\mathrm{}\pm 0.2$ Mc/sec and $b=24.4\mathrm{}\pm 1.3$ Mc/sec, and for the $5P_{\frac{1}{2}}$ state, $a_{\frac{1}{2}}=120.7\mathrm{}\pm 1$ Mc/sec. For ${\mathrm{Rb}}^{87}$, the three constants are $a_{\frac{3}{2}}=85.8\mathrm{}\pm 0.7$ Mc/sec, $b=11.8\mathrm{}\pm 0.6$ Mc/sec, and $a_{\frac{1}{2}}=409\mathrm{}\pm 4$ Mc/sec. The quadrupole moments are $Q_{85}=(0.27\mathrm{}\pm 0.02)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ and $Q_{87}=(0.13\mathrm{}\pm 0.01)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$, which agree with the moments calculated from the hyperfine structure of these isotopes in the $6P$ state as measured by another technique.