Relative Intensities of Singlet-Singlet and Singlet-Triplet Transitions

The ratio of the intensities of singlet-triplet to singlet-singlet transitions can be calculated by means of Houston's formulae in two ways: (a) from the deviations from the interval rule, and (b) from the distance of the singlet level from the center of gravity of the triplet levels. The discrepancy of the two calculations indicates that the integral of the radial functions between the singlet and triplet differs from that for the triplet with triplet, say by a factor $\lambda$. The new parameter $\lambda$ is evaluated (∼0.75) from the positions of the four levels, and gives intensity ratios in good agreement with the observed.