Experiments on the 2 3P state of helium. IV. Measurement of the 2 3P0-2 3P2 fine-structure interval

The 2 ³P₀-2 ³P₂ fine-structure interval ν₀₂ has been measured using the optical-microwave atomic beam magnetic resonance technique with the result ν₀₂=31 908.040 (20) MHz (0.6 ppm). This is in excellent agreement with the sum of previous separate measurements of the 2 ³P₀-2 ³P₁ and 2 ³P₁-2 ³P₂ intervals, which gives ν₀₂=31 908.060 (36) MHz, and establishes internal consistency for all the measurements. The most accurate comparison with theory is for ν₀₁, and we obtain the most accurate experimental value for this by subtracting the earlier measurement of ν₁₂ from the present result for ν₀₂. The result is ν₀₁=29 616.844+/-0.021 MHz (0.7 ppm) (experiment) compared to ν₀₁=29 616.914+/-0.043 MHz (1.5 ppm) (theory). Alternatively our experiment can be regarded as an independent measurement of the fine-structure constant with the result α^-1=137.036 12 (11) (0.8 ppm) which is consistent with the more accurate currently accepted value α^-1=137.035 963 (15) (0.11 ppm).