The intensity distribution in progressions of the big mode observed in phosphcrescence and phosphorescence-excitation spectra of p) mzine is interprered m terms of a model mvohin~ vrbronic couplin: in both singlet and triplet manifolds mediated by spin-orbit coupling. Pyrazine has been used repeatedly [l-l I] to illustrate vlbronic coupling effects in moleculsr spectroscopy-The relatively strong vibronic coupling between St = iB3u(nrr*) and S, = lB,u(~~*) through mode vIOs(bIg) is well understood 12-41 I here the coupling is strong enough to cause vIfi progressions in absorption and fluorescence spectra with anomaIous, zmharmonic level spscings in the S, and (presumably) S, manifolds [7-g]_ The triplet T, = 3 Bxu(rm*) band svstem shows similar anomalous spacings, presumably due to vibronic coupling with T, = 3B2u(nz*) [5,6,!0,1 I] _ However the vtoa intensity patterns in the phosphorescence and phosphorescence-excitation spectra are quite different from those in &he fluorescence and absorption spectra of pyrazine_ In this note we will show that the tripiet intensity pattern cannot be understood sole-Iy on the basis of vibronic coupling but requires superpo-ition of vxbronic and spin-orbit coupling_ Since the So-T, transition is multiplicityforbidden, it derives Intensity from ailowed transitions through spin-orbit coupling_ NegIecring couplings invoIving the ground state, we expect So +-T, to derive most of its intensity from So + S2, since the spin-orbit coupling is strongest between mr* and xx* states. This direct mechanism yields intensity * Issued as NRCC No. 17677.