Fine and hyperfine structure of ortho-H2, k(4p) 3πu

The MOMRIE (microwave optical magnetic resonance induced by electrons) spectrum has been observed and measured for ortho‐H₂, k(4p) ³π_u, in the lowest four vibrational levels ν = 0−3, and the lowest rotational level, N = 1. The best data are obtained for ν = 1 and 3; the ν = 0 data suffer from severe electric field broadening and the ν = 2 data are affected by a large but undetermined perturbation. Analysis yields values for the spin‐orbit and spin‐spin coupling constants, the orbital angular momentum and dipolar hyperfine constants, the orbital g factor, and the magnetic and electric susceptibilities. These parameters are then ``corrected'' for the breakdown of the Born‐Oppenheimer approximation by the same procedures previously applied to the d(3p) ³π_u state. The present results are combined with previous work on the n p ³π_u Rydberg series [the c(2p) ³π_u and d(3p) ³π_u states of H₂ and the X ${}^2{\Sigma }_{\mathrm{g}}^{+}$ state of ${\mathrm{H}}_2^{+}$ ] to illustrate the variation of fine and hyperfine structure parameters with the principal quantum number, and the deviation of molecular Rydberg states from the united atom model.