Anticrossings and microwave transitions between electronic states of H2

Abstract

Electric field induced anticrossings and electric dipole microwave transitions have been observed between the d(3p) ³Π_u, v=3, N=1 level and the i(3d) ³Π_g, v=3, N=2 level of para H₂. These observed signals correspond to normally forbidden changes in the electron spin magnetic quantum number M_S of ±1 or ±2. They are weakly allowed, however, at the magnetic fields used (7 to 13 kG), because the electron spin S is not completely decoupled from the rotational motion N. The zero field separation between the levels is 1.9244±0.0007 cm⁻¹, significantly larger than the optically determined value of 1.82 cm⁻¹. The fine structure and Zeeman effect of the d(3p) ³Π_u state are accurately known from previous work. In the i(3d) ³Π_g, v=3, N=2 level, g_N is measured to be −0.2202±0.0012, a value largely determined by L uncoupling in the (3d)³(Σ,Π,Δ)_g complex but also influenced by unidentified perturbations. The measured spin‐orbit and spin‐spin interaction values are marginally significant, but they are needed to fit the data and are not inconsistent with estimates of their values.