10, 10-dimethylanthracen-9-one single crystal emission and absorption spectra have been recorded at low temperatures, as well as Raman spectra on the melt. The absorption spectra of both the lowest triplet and lowest excited singlet states clearly show the absorption origins of the three different molecular sites in the triclinic unit cell of the crystal. The emission spectra indicate that substantial spin-orbit/vibronic state mixing occurs, giving rise to transitions between the z sub-level of the lowest 3nπ‡ state (T1) and both totally and non-totally symmetric vibrations of the ground state. The preferred intensity stealing route is from T1 (z) to S2(1ππ‡) by spin-orbit coupling with vibronic mixing of S3 and S4(1ππ‡, 1B2). © 1982.