Metastable a ³II ¹³CO: Molecular-beam electric-resonance measurements of the fine structure, hyperfine structure, and dipole moment

The radio-frequency spectrum of metastable a ³II ¹³CO has been measured in molecular-beam electric resonance in the range 0-2000 MHz. Electric-dipole transitions with ΔJ = 0 and ΔF = 0, ±1 have been observed in states |v,Ω J, F| = |0-3, 1-2, 1-7, J±2 ) at zero field. The set of transitions in each vibrational state has been analyzed to give three parameters describing the lowest-order magnetic hyperfine interactions of the ¹³C nuclear spin (I = 1/2) with the spin (S) and orbital (L) angular momenta of the two unpaired electrons in the 5σr2Π open-shell configuration. The vibrational dependence of the measured hyperfine parameters is fitted to a polynomial in (v+1/2)ⁿ to give: Origin Parameter Value at R_e(a³II) (in MHz) I·S Fermi contact K = 1935.1±0.5 I·S spin-spin dipole D^δ = 106.5±0.1 D = 7.9±0.1 I·L spin-orbital G = 162.5±0.1 Restricted Hartree-Fock calculations of these hyperfine terms are in good agreement with the measured values. The Stark effect has been measured in states | v, Ω, J, F)=| 0-3, 2, 2-3, J+1/2| of a³II¹³CO to give dipole moments which display a slight non vibrational isotopic shift (l in 10⁴) from the moments measured in the corresponding states | v, Ω, J| of a ³II ¹²CO.