Knowledge Bank

The technique of selectively detected fluorescence excitation spectroscopy has been used to analyze two forbidden $d3\Phi 3-$ and $a3\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Delta 3$ and $e3\Phi 3-a41\Delta 2$ transitions of LaF. The principal constants (in $cm-1$) obtained from recent and $previous1-2$ analyses are: [FIGURE] The multiplet splittings for the triplet states shows that case (a) LS coupling is a better approximation for the LaF triplet states than case (c) j-j coupling. This is in contrast to the situation for the isoclectronic molecule CcO,where j-j coupling is suitable for states arising from the 4f6s configuration. Ligand field theory calculations have been used in an attempt to provide configurational assignments for the excited states.