The hyperfine structure of the ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ ground states of ${\mathrm{Cl}}^{35}$ and ${\mathrm{Cl}}^{37}$ is investigated by the atomic beam magnetic resonance method. Values of the magnetic dipole interaction constant, $a$, and the electric quadrupole interaction constant $b$ are found to be $a_{35}=205.288\mathrm{}\pm 0.010$ Mc/sec., $a_{37}=170.686\mathrm{}\pm 0.010$ Mc/sec., $b_{35}=55.347\mathrm{}\pm 0.020$ Mc/sec., $b_{37}=43.256\mathrm{}\pm 0.020$ Mc/sec.

No octupole interaction is required to account for the experimental results. A simple method is introduced for calculating accurate values of the electric quadrupole moments $Q$ from these data and the corresponding values are $Q_{35}=-(0.0795\mathrm{}\pm 0.0005)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ and $Q_{37}=-(0.0621\mathrm{}\pm 0.0005)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$.

This method can be extended to many other cases for which the interaction constants $a$ and $b$ and the nuclear gyromagnetic ratio are known. Experimental details are given for the production and detection of beams of atomic chlorine.

• Received 12 July 1949

DOI:https://doi.org/10.1103/PhysRev.76.1076