Fine structure of para-H2 d(3p) 3Πu (ν = 0–3) via microwave optical magnetic resonance induced by electrons

The MOMRIE (microwave optical magnetic resonance induced by electrons) spectrum of ${\mathrm{para‐H}}_2{\text{\hspace{0.17em}d(3p)\hspace{0.17em}}}^3{\Pi }_u$ has been measured in vibrational levels ν = 0–3 for the lowest rotational state (N = 1). The theory previously used to analyze the MOMRIE spectrum of ortho‐H₂ is also used here, but with the addition of terms to account for the effects of the magnetic and electric susceptibilities. Least squares fits of the MOMRIE spectral lines provide values of the so‐called spin‐orbit and spin‐spin coupling constants, the orbital g factor, and the susceptibilities. Comparison of these values with corresponding values for ortho‐H₂ reveals significant breakdown of the Born‐Oppenheimer approximation. Zero field fine structure separations and level crossing magnetic fields have been calculated from the molecular parameters. They agree with previous experimental measurements but are considerably more extensive and more accurate. The radiative lifetime, as determined from the MOMRIE linewidth, is 29.4±3.2 nsec.