The theory of the fine structure of ${\mathrm{O}}_2$ is made somewhat more complete and fitted to the observed microwave spectrum. This gives $B_0=43\mathrm{}102\pm 5$ Mc/sec for ${\mathrm{O}}^{16}$${\mathrm{O}}^{16}$. In addition there is evidence for the effect of higher order terms such as centrifugal distortion on the magnetic interaction constants. Magnetic hyperfine structure has been observed in the spectrum of ${\mathrm{O}}^{16}$${\mathrm{O}}^{17}$. The spectrum agrees with that predicted on the basis of a perturbation Hamiltonian $b\mathrm{I}·\mathrm{S}+c{I}_z{S}_z$, where $b=-102\mathrm{}$ Mc/sec and $c=140\mathrm{}$ Mc/sec. The value of 5/2 for the spin of ${\mathrm{O}}^{17}$ is confirmed.

• Received 12 January 1953

DOI:https://doi.org/10.1103/PhysRev.90.537