MOLECULAR-BEAM LASER SPECTROSCOPY OF LANTHANUM MONOFLUORIDE - MAGNETIC HYPERFINE AND DIPOLE-MOMENT MEASUREMENTS

The lanthanum monofluoride molecule (LaF) was generated in a pulsed molecular beam by chemical reaction in a laser-produced plasma. The (0,0) and (1,0) bands of the B1PI-X1SIGMA+ system of LaF (nu00= 16 184.52 cm-1), and the 0+-X1SIGMA+ band (nu00 = 16 637.95 cm-1), were investigated at sub-Doppler resolution (120 MHz) using a ring dye laser to excite fluorescence. The electron orbital-nuclear spin interaction parameter (magnetic hyperfine a parameter) was determined to be +138 (5) MHz and +149 (5) MHz for the v = 0 and v = 1 levels of the B1PI state, respectively (2sigma error bounds). The observed hyperfine structure is interpreted in terms of ligand field theory. Molecular rotational constants for all three bands were found to be in good agreement with previous work [Schall et al, J. Mol. Spectrosc. 100, 437 (1983)]. The permanent electric dipole moments of the X1SIGMA+ and 0+ states of LaF were determined by molecular-beam Stark spectroscopy to be 1.808(21) D and 3.43(10) D (2sigma errors). Results are compared with recent experimental determinations of the dipole moments of the other group III monofluorides.