Identification of some diffuse interstellar features

Abstract

Twenty-eight of the thirty-nine diffuse interstellar bands identified by Herbig (1975) are shown to constitute three vibronic systems with origins at 14 321, 15 153, and 15 343 cm−1 (vac). Structure within these three systems arises from the excitation of vibrational modes withv1=275 cm−1,v2=445.5 cm−1, andv3=793 cm−1. The electronic origins at 14 321 and 15 343 cm−1 correspond to narrow lines observed in the spectrum of Cr3+ ions at cubic sites in MgO solids while the 15 153 cm−1 origin arises in Mn4+ : MgO. Hence, many of the diffuse bands in the visible likely are due to small MgO particles containing these ions. This observation is compatible with recent experimental data showing broad bands at 160 nm and 220 nm from finely divided MgO solids that match features in the interstellar extinction curve.