Separated oscillatory-field microwave measurement of the 2 3P1-2 3P2 fine-structure interval of atomic helium

The 2 P-3(1)-2 P-3(2) interval in helium is measured using microwave separated oscillatory fields. Our measured result is 2 291 177.53 +/- 0.35 kHz . A disagreement with theory of over 15 kHz indicates a major problem with two-electron QED calculations. If this disagreement is resolved, measurements of both 2 P-3 fine-structure intervals at this accuracy would lead to a six-parts-per-billion determination of the fine-structure constant.