Experiments on the $2 {}^{3}P$ state of helium. IV. Measurement of the $2 {}^{3}P_{0} - 2 {}^{3}P_{2}$ fine-structure interval

The

2 {}^{3}P_{0} - 2 {}^{3}P_{2}

fine-structure interval

ν_{02}

has been measured using the optical-microwave atomic beam magnetic resonance technique with the result

ν_{02} = 31 908.040

(20) MHz (0.6 ppm). This is in excellent agreement with the sum of previous separate measurements of the

2 {}^{3}P_{0} - 2 {}^{3}P_{1}

and

2 {}^{3}P_{1} - 2 {}^{3}P_{2}

intervals, which gives

ν_{02} = 31 908.060

(36) MHz, and establishes internal consistency for all the measurements. The most accurate comparison with theory is for

ν_{01}

, and we obtain the most accurate experimental value for this by subtracting the earlier measurement of

ν_{12}

from the present result for

ν_{02}

. The result is

ν_{01} = 29 616.844 \pm 0.021

MHz (0.7 ppm) (experiment) compared to

ν_{01} = 29 616.914 \pm 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).

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Experiments on the2P3state of helium. IV. Measurement of the2P03−2P23fine-structure interval