15min:

WILTON L. VIRGO AND TIMOTHY C. STEIMLE, Department of Chemistry and Biochemistry, \linebreak Arizona State University, Tempe, AZ, 85287-1604.

The optical Stark effect in the (0,0) A² _3/2-X^{2 +},A² _1/2-X^{2 +} and B^{2 +}-X^{2 +} band systems of a lanthanum monoxide, LaO, supersonic molecular beam sample have been analyzed to produce permanent electric dipole moments, µ, for the A² _3/2,A² _1/2 and B^{2 +} 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 _ 3/2-X^{2 +} and A² _1/2-X^{2 +} 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 X^{2 +}, A² _1/2, A² _3/2 and B^{2 +} 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.
[.25in] \noindent 1. R.F. Seunram, F.J. Lovas, G.T. Fraser and K. Matsumura, J. Chem. Phys. 92, 4724 (1990).