On a vibronic origin for the diffuse band spectrum

Duley (1982) has proposed that many of the diffuse interstellar bands in the wavelength interval 677 nm>λ>542 nm arise from vibronic transitions of Cr³⁺ ions in MgO grains. No explanation has been offered for the fact that as many as 85 of the possible 108 transitions of this system have not been observed in the interstellar medium. Moreover, the relative intensities of the diffuse bands which are observed appear to be inconsistent with their assignment. We therefore conclude that this model is not consistent with the observations.