Molecular-Beam Electric-Resonance Spectroscopy of the a 3Π (υ = 4)−a′ 3Σ+ (υ′ = 0) Perturbation in CO

The heterogeneous perturbation of the a 3Π (υ = 4) state of CO by the nearly degenerate a′ 3Σ+ (υ′ = 0) state is observed in the rf electric–dipole spectrum of the metastable a 3Π (υ = 4) state. Perturbed lambda doublings and Stark effects in states | υ, Ω, J〉 = | 4, 2, 2–6〉 have been measured in molecular-beam electric resonance from 7–400 MHz. These measurements are combined with existing optical data to obtain the off-diagonal matrix elements of the fine structure which describe the a–a′ interaction, 〈a 3Π ‖ AL+ / 2 ‖ a′ 3Σ+〉 = − 18.1 ± 0.3 cm−1, 〈a 3Π ‖ BL+ ‖ a′ 3Σ+〉 = 0.16 ± 0.01 cm−1, and the diagonal and off-diagonal components of the dipole moment, 〈a 3Π ‖ μ ‖ a 3Π〉 = 1.3791 ± 0.0003 D, 〈a 3Π ‖ μ ‖ a′ 3Σ+〉 = 0.62 ± 0.02 D. This last quantity is identically the electronic transition moment of the (a′ 3Σ+−a 3Π) Asundi system.