Spin and Hyperfine Structure of Arsenic-76

Hyperfine structure in the ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ ground state of the radioactive atom ${\mathrm{As}}^{76}$ has been investigated by the method of magnetic resonance in an atomic beam produced by microwave discharge dissociation of arsenic vapor. $\Delta F=0\mathrm{}$ resonances were observed within both the $F=\frac{5}{2}$ and $F=\frac{7}{2}$ atomic levels at several values of magnetic field up to about 5 oe, indicating that the spin of the ${\mathrm{As}}^{76}$ nucleus is 2. An analysis of multiple quantum transition spectra within the same $F$ states gave a measurement for two of the hfs intervals: $\Delta {\nu }_{\frac{7}{2},\frac{5}{2}}=\pm (117\mathrm{}\pm 4)$ Mc/sec and $\Delta {\nu }_{\frac{5}{2},\frac{3}{2}}=\pm (69\mathrm{}\pm 16)$ Mc/sec, with the same sign for both. From the value of the hfs constant $A$, the magnitude of the magnetic field at the arsenic nucleus is (1.33±0.15)×${10}^5$ oe in reasonable agreement with the variation in this field among similar atoms. The value of $g_J$ has been found to be 1.994±0.003 for arsenic.