Measurement of the2S122−2P322Interval in Atomic Hydrogen

An experiment is described in which the two transitions $\alpha a(m_J=+\frac{1}{2}\to +\frac{3}{2})$ and $\alpha b(m_J=+\frac{1}{2}\to +\frac{1}{2})$ were employed to measure the interval ${(\Delta E-\mathcal{S})}_{\mathrm{H}}$. Hydrogen atoms in the metastable state are produced by bombarding molecular hydrogen with electrons within a waveguide in a magnetic field. An rf electric field in the guide induces electric dipole transitions from this state to the $2P$ states, and the 1216-Å radiation produced in the decay of the $2P$ state is detected. The frequency of the rf field is held constant, and the magnetic sublevels of the states involved are tuned by varying the magnetic field. When the resonance condition is met, the intensity of 1216-Å light increases. Precision measurements of signal versus magnetic field are fitted by least squares to a line-shape formula described in detail. Potential sources of systematic error and experimental searches for them are described. Small shifts are detected upon changing the electron-beam current and gas pressure, and an extrapolation is made to remove them. The weighted average of results from the two transitions is ${(\Delta E-\mathcal{S})}_{\mathrm{H}}=9911.377\mathrm{}\left(26\right)\mathrm{}$ MHz. A comparison is made with other recent experiments which have measured the same interval.