Stark-Zeeman effect of metastable orthohydrogen and parahydrogen

The Stark effect of the N = 1 rotational level in the metastable c 3Pi/subu/ electronic state of orthohydrogen has been measured using the molecular-beam magnetic-resonance method. The Stark-shift coefficients of orthohydrogen, unlike those of parahydrogen, are strongly dependent on static magnetic field strength. The measured magnetic field dependence of these coefficients agrees with a calculation in which we assume that the major contribution to this phenomenon is the mixing of hyperfine levels by the Zeeman-effect perturbation. The extrapolated zero-magnetic-field values of the Stark-shift coefficients are in reasonable agreement with the corresponding theoretical values. The Stark effect of the N = 2 rotational level of parahydrogen has been remeasured with considerable reduction in the experimental uncertainties. This allows a more meaningful comparison with theory. At large magnetic field strengths (100--150 G) the Stark effect of para-H2 exhibits a small dependence on magnetic field which is due to mixing of the fine-structure levels by the Zeeman-effect perturbation