Theory of Singlet—Triplet Transitions in Magnetic Rotation Spectra

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Abstract
The theory of the resonance fluorescence of degenerate or near-degenerate states is derived and it is applied to a description of magnetic rotation spectra of triplet—singlet transitions. The transition probability is obtained as a quotient of two determinants, each containing the matrix of the damping constants between the different states. The mathematical formalism becomes reasonably simple only if the energy differences between the states are large with respect to the absolute values of the off-diagonal damping constants. Therefore our results for the magnetic rotation spectra of triplet—singlet transitions are restricted to the case of large magnetic fields so that the splittings of the triplet levels are large compared to the natural line breadths of their absorption lines. It is found that the relative intensities of singlet—triplet transitions in magnetic rotation spectra are compatible with or even larger than the intensities of singlet—singlet transitions. The possible importance of spin—spin interactions is mentioned.