The Zeeman effect in spin-allowed and forbidden doublet-doublet transitions in orthorhombic rotating molecules

Theoretical predictions of the Zeeman effect on spin-allowed and forbidden doublet-doublet transitions in near-symmetric top molecules are reported, with the assistance of computer simulations of band profiles. Bandwidths in the high-field limit have been determined. Marked differences have been found between the behavior of spin-allowed and forbidden transitions. The intermediate-field effect on spin-allowed transitions is sensitive to the relative energy order of the zero-field spin components of the rotational sublevels in the combining vibronic states. In the high-field limit the rotational components of spin-allowed transitions give rise to a single band, corresponding to ΔM_S = 0, whereas the bands with ΔM_S = ±1 are also expected in spin-forbidden transitions. The applicability to actual cases is finally discussed.