Born-Oppenheimer breakdown and isotope effects in 3Π electronic states

Abstract

Recent MOMRIE (microwave optical magnetic resonance induced by electrons) experiments on the d (3p) ³Π_u state of ortho‐ and para‐H₂ and D₂ have revealed discrepancies in measured fine structure parameters (spin‐orbit and spin‐spin coupling constants, etc.) which are inexplicable in terms of the Born‐Oppenheimer approximation. A general theory is developed to account for the effect of homogeneous and heterogeneous perturbations, both regular and irregular, upon the measured fine structure constants of a ³Π electronic state. In particular the various perturbations' mass and symmetry dependences are determined. To make the theory applicable to an analysis of the experimental results for the d(3p) ³Π_u states of H₂ and D₂, other mass dependent effects‐adiabatic, Born‐Oppenheimer isotope, and vibrational‐which alter fine structure are also considered.