We have measured the hyperfine structure in the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ states of the ground state configuration of ${\mathrm{C}}^{11}$ by the atomic-beam magnetic-resonance technique. The values obtained after corrections for perturbations by nearby fine-structure states are ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$: $\frac{A}{h}=(-)68.203\pm 0.007$ Mc/sec, $\frac{B}{h}=(-)4.949\pm 0.028$ Mc/sec; ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$: $\frac{A}{h}=(-)1.242\pm 0.010 \mathrm{Mc}/sec or \mathrm{}(-)1.200\pm 0.010 \mathrm{Mc}/sec$ depending upon the choice of zero-field level ordering, where $B(J=1\mathrm{})=-\frac{B(J=2\mathrm{})\mathrm{}}{2}$. From these data it is possible to calculate the nuclear moments of the mirror nucleus, ${\mathrm{C}}^{11}$, using a theoretical value of $〈\frac{1}{r^3}〉$ for the $p$ electrons. The results are ${\mu }_I=(-)1.027\pm 0.010$ nm, $Q_{\mathrm{uncorrected}}=(+)(0.0308\mathrm{}\pm 0.0006)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. No signs were measured in these experiments; the indicated signs assume ${\mu }_I<0\mathrm{}$ in ${\mathrm{C}}^{11}$. A value of 1.5011±0.0006 for $g_J$ was also obtained in the ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ state.

• Received 19 June 1964

DOI:https://doi.org/10.1103/PhysRev.136.B932