Experiments on the2P3state of helium. III. Measurement of the2P03−2P13fine-structure interval

Abstract

The $2{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}-2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ fine-structure interval ${\nu }_{01}$ has been measured using the optical-microwave atomic beam magnetic resonance technique. The result, a major improvement upon previous measurements, is ${\nu }_{01}=29\mathrm{}616.864\pm 0.036$ MHz (1.2 ppm). This compares well with the latest theoretical value ${\nu }_{01}=29\mathrm{}616.914\pm 0.043$ MHz (1.4 ppm), and provides an important test of the theory of fine structure of the two-electron atom. Alternatively, our experiment can be regarded as an independent measurement of the fine-structure constant with the result ${\alpha }^{-1\mathrm{}}=137.036\mathrm{}08\pm 0.00013$ (0.94 ppm), which is consistent with the more accurate currently accepted value ${\alpha }^{-1\mathrm{}}=137.035\mathrm{}963\pm 0.000015$ (0.11 ppm).