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

The heterogeneous perturbation of the $a^3\text{Π (υ\hspace{0.17em}=\hspace{0.17em}4)}$ state of CO by the nearly degenerate ${\mathrm{a\prime }}^3{\Sigma }^{+}\text{(υ′\hspace{0.17em}=\hspace{0.17em}0)}$ state is observed in the rf electric–dipole spectrum of the metastable $a^3\text{Π (υ\hspace{0.17em}=\hspace{0.17em}4)}$ state. Perturbed lambda doublings and Stark effects in states $\text{|\hspace{0.17em}υ, Ω, J〉\hspace{0.17em}=\hspace{0.17em}|\hspace{0.17em}4, 2, 2–6〉}$ 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 $\mathrm{a–a\prime }$ interaction, ${\mathrm{〈a}}^3{\mathrm{\Pi \hspace{0.17em}\Vert \hspace{0.17em}AL}}_{+}{\text{\hspace{0.17em}/\hspace{0.17em}2\hspace{0.17em}‖\hspace{0.17em}a′}}^3{\Sigma }^{+}\text{〉\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}18.1\hspace{0.17em}±\hspace{0.17em}0.3}{\mathrm{cm}}^{\text{−1}}{\mathrm{,\; 〈a}}^3{\mathrm{\Pi \hspace{0.17em}\Vert \hspace{0.17em}BL}}_{+}{\mathrm{\hspace{0.17em}\Vert \hspace{0.17em}a\prime }}^3{\Sigma }^{+}\text{〉\hspace{0.17em}=\hspace{0.17em}0.16\hspace{0.17em}±\hspace{0.17em}0.01}{\mathrm{cm}}^{\text{−1}}$ , and the diagonal and off‐diagonal components of the dipole moment, ${\mathrm{〈a}}^3{\mathrm{\Pi \hspace{0.17em}\Vert \hspace{0.17em}\mu \hspace{0.17em}\Vert \hspace{0.17em}a}}^3{\text{Π〉\hspace{0.17em}=\hspace{0.17em}1.3791\hspace{0.17em}±\hspace{0.17em}0.0003 D, 〈a}}^3{\mathrm{\Pi \hspace{0.17em}\Vert \hspace{0.17em}\mu \hspace{0.17em}\Vert \hspace{0.17em}a\prime }}^3{\Sigma }^{+}\text{〉\hspace{0.17em}=\hspace{0.17em}0.62\hspace{0.17em}±\hspace{0.17em}0.02 D}$ . This last quantity is identically the electronic transition moment of the ${\mathrm{(a\prime }}^3{\Sigma }^{+}{\mathrm{-a}}^3\mathrm{\Pi )}$ Asundi system.