Hyperfine Splittings and Pressure Shifts ofLi6andLi7

The spin-exchange optical-pumping technique has been used to measure the hyperfine splittings in the ground states of ${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$ as a function of buffer-gas pressure. Measurements were made with He, Ne, and Ar buffer gases at temperatures near 390°C. The fractional pressure shifts for Li were found to be (-5.34±0.5) × ${10}^{-9\mathrm{}}$ /Torr in Ar, (40.5 ± 1.0) × ${10}^{-9\mathrm{}}$ /Torr in Ne, and (77.7±1.0) × ${10}^{-9\mathrm{}}$ /Torr in He. The hyperfine splittings extrapolated to zero pressure are 228.205 261 (12) MHz for ${\mathrm{Li}}^6$ and 803.504 094 (25) MHz for ${\mathrm{Li}}^7$.