Hyperfine Structure ofK39in the4PState

The atomic-beam magnetic resonance method has been used to investigate the hyperfine structure of the $4P$ state of ${\mathrm{K}}^{39}$. The apparatus and method of observation were similar to those used in previous experiments on sodium, rubidium, and cesium. For ${\mathrm{K}}^{39}$, the magnetic-dipole interaction constant in the $4P_{\frac{1}{2}}$ state is $a_{\frac{1}{2}}=28.85\mathrm{}\pm 0.3$ Mc/sec, the electric-quadrupole interaction constant in the $4P_{\frac{3}{2}}$ state is $b=2.8\mathrm{}\pm 0.8$ Mc/sec, and the quadrupole moment is (0.07±0.02)×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$.