Hyperfine Structure of the Ground State ofMn55

The five hyperfine transition frequencies of the $S_{\frac{5}{2}}$ ground state of ${\mathrm{Mn}}^{55}$ have been measured in a spin-exchange optical pumping experiment. The optical pumping flasks contained a neon buffer gas, and the measurements were made as a function of buffer-gas pressure. The measurements were carried out at a temperature of 700 °C. The linewidth of the Mn signal was typically 300 Hz. The hyperfine interaction constants were found to be $A=-72420836\mathrm{}\left(15\right)\mathrm{}$ Hz, $B=-19031\mathrm{}\left(17\right)\mathrm{}$ Hz, $C=-0.7\mathrm{}\pm 1.1$ Hz, $\mathrm{}\left|D\right|<0.25\mathrm{}$ Hz, and $\mathrm{}\left|E\right|<0.02\mathrm{}$ Hz. The fractional pressure shift in $A$ was found to be $\left(\frac{1}{A}\right)\left(\frac{\partial A}{\partial P}\right)=(2.6\mathrm{}\pm 0.2)\times {10}^{-8\mathrm{}}$ ${\mathrm{Torr}}^{-1\mathrm{}}$. No pressure dependence of the other interaction constants was observed.