Knowledge Bank

The optical Stark effect in the $(0,0)A2\Pi 3/2-X2\Sigma +,A2\Pi 1/2-X2\Sigma +$ and $B2\Sigma +-X2\Sigma +$ band systems of a lanthanum monoxide, LaO, supersonic molecular beam sample have been analyzed to produce permanent electric dipole moments, $\mu$, for the $A2\Pi 3/2,A2\Pi 1/2$ and $B2\Sigma +$ states of 1.89(6)D, 2.44(2)D and 0.2(1)D, respectively. The ground state dipole moment was determined some time $ago1$ to be 3.207(11)D. Fine structure splitting in the field free $A2\Pi 3/2-X2\Sigma +$ and $A2\Pi 1/2-X2\Sigma +$ spectra was analyzed to produce the magnetic hyperfine spectroscopic parameters a = 233(4) MHz, c = -261(12) MHz, and d = 410(4) MHz. The Group IIIA monoxides, ScO, YO and LaO are prototypical examples of transition metal-oxide bonded molecules. This work on LaO has resulted in the first complete set of dipole moment measurements for the $X2\Sigma +,A2\Pi 1/2,A2\Pi 3/2$ and $B2\Sigma +$ states for any of these monoxides. The permanent electric dipole moments for the low-lying states of LaO are exceedingly small, given that they are conventionally viewed as having a $La+2O-2$ charge distribution and exhibiting a large variation amongst the four states.