Microwave spectroscopy of MgO in the a3Π and X1Σ states

Pure rotational transitions of MgO in the a3Πi state and the ground X1Σ+ state (v=1–3) were observed in the 210–400 GHz region. The MgO molecule was produced by a DC discharge in a mixture of Mg vapor and N2O. A simultaneous deperturbation analysis for the X1Σ+, a3Π, and A1Π states was carried out for the observed transition frequencies including previous high-resolution data, where the energy levels were calculated by diagonalizing the energy matrix including the spin–orbit and orbit–rotation interactions among three electronic states with vibrational levels up to v=9. A centrifugal term of the spin–orbit interaction between the a3Πi and X1Σ+ states was newly introduced to improve quality of the fitting, to explain the observed Λ-type doubling of the a3Πi state.