THE ELECTRIC DIPOLE MOMENT OF YTTERBIUM MONOXIDE

$^{g}$ C. Linton, S. McDonald, S. Rice, M. Dulick, Y. C. Liu And R. W. Field, J. Mol Spectrosc. \textbf{101}, 332 (1983). $^{h}$ M. Dolg, H. Stoll and H. Preuss, Theor. Chim. Acta. \textbf{85}, 441 (1993).Author Institution: Physics Department, University of New Brunswick; Department of Chemistry and Biochemistry, Arizona State UniversityPrevious experimental spectroscopic $data^{g}$ on the ytterbium monoxide molecule, YbO has indicated that the ground state is a $^{1}\Sigma^{+}$ state originating from the closed $4f^{14}$ configuration of the $Yb^{+2}$ ion. Ab initio $calculations^{h}$ have consistently placed the low-lying states of the $4f^{13}$ 6s superconfiguration below that of the $4f^{14}$ configuration. The $4f^{13}$ 6s superconfiguration is expected to have the smaller dipole moment because of the large back-sided polarization of the 6s orbital. We therefore decided to try and measure the dipole moment in an attempt to resolve this issue and gain a better understanding of the configurational nature of the ground state. A supersonic molecular beam of ytterbium monoxide, YbO, was produced by reacting Yb atoms with oxygen in a laser ablation source, passing the beam through a pair of Stark plates and applying an electric field. The beam was interrogated by a single mode ring dye laser tuned to the R(1) line of the $\Omega = 0^{+} - X^{1}\Sigma^{+}$ transition at 579 nm and, from the Stark shifts of the lines, a dipole moment of $\sim 5.8$ Debye was determined for both states. The details of this investigation will be presented and the results discussed in terms of the electron configurations of the two states