[en] A new method for determination of relative dipole matrix elements for transitions between excited states is presented, using sum frequency generation spectroscopy. The method is based on measuring the frequency spacing of related extrema in the dispersion like shapes within the SFG-spectrum, caused by interference between resonant and nonresonant parts in the third order polarizability. It is applied to CdI with the generated frequency in the range of the principal series 5s¹S₀->np¹P₁, n=12-28. Values of the products μsub(6snp)μsub(np5s) are presented obeying the nsup(*-3) law. (orig.)