General Discussion: Electronic Emission Spectroscopy of CFFormula and SiFFormula: Appendix. The Sign of the Spin-Orbit Coupling Constant in (tFormula States of AXFormula Ions

The spin-orbit splitting in orbitally degenerate systems with one open shell usually conforms to Hund’s third rule: that is, the splitting is regular for a less than half-filled shell, and inverted for a more than half-filled shell. The C2T2 states of CF+4 and SiF+4 reported by Mason & Tuckett violate this expectation. We show below how this may occur in AX+4 ions where the dominant atomic spin-orbit coupling arises from motion around the X atoms.