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Cluster models are constructed for mono- and dinuclear Cr(II) sites and mononuclear Cr(III) sites on the Cr/SiO2 Phillips catalyst and used to compute d–d transition energies and intensities. Mononuclear pseudo-tetrahedral Cr(II) gives rise to two bands of electric-dipole-allowed d–d transitions, at 8,400 and 12,300 cm−1. This doublet is lowered in energy and intensity as the bond angle about chromium, ∠OCrO, opens up. The dinuclear site gives rise to bands at 5,200 and 10,300 cm−1, consistent with calculations for a mononuclear cluster of comparable value for ∠OCrO. A tri-coordinated Cr(III) cluster shows bands of comparable oscillator strengths at energies of 11,000, 16,000, 18,000–20,000 and 33,000 cm−1. The predicted bands correspond well with d–d bands in experimental diffuse reflectance spectra.