The lowest triplet state of tetramethyl-1,3-cyclobutanedithione. III. Single-crystal Zeeman spectroscopy

Abstract Pulsed, high-field Zeeman spectra of the lowest singlet-to-triplet transition in single-crystal tetramethyl-1,3-cyclobutanedithione (TMCBDT) have been measured. The analysis of the spectra was performed using an extension of the theory of Castro and Hochstrasser which allows for an arbitrary alignment of the magnetic field with respect to the principal crystal axes. From this study we provide evidence that in TMCBDT (1) the lowest triplet is 3 A u (D 2h molecular symmetry). (2) only one spin-orbit coupling route is active. (3) a substantial zero-field splitting (2.5 ± 1.0 cm −1 ) is present. (4) the magnetic and molecular axes are rotated by 90°. and (5) the spin-orbit contribution to the triplet-state g values is small compared to its effect on the zero-field splitting parameters.