A survey of weak diffuse interstellar bands in selected ranges between 5600 and 7000 Å

The paper describes briefly the history of the discovery of diffuse interstellar bands (D] Bs) and their "younger relatives", weak unidentified interstellar features, recently, discovered and described in scientific literature. The features of both kinds form a verv rich spectrum of interstellar clouds, the spectrum varying, however, from object to object. The high quality echetle spectra acquired at McDonald Observatory (R = 60,000 ; S/N = 500) indicate that both strong and weak features form several subsets ("families") which can be considered as spectra of single species populating the interstellar clouds. This fact is important as any two of the well-known. strong DlBs hardly belong to one such "family" which makes the identification of the DIB carriers so difficult. The paper also discusses the difficulties of the detection of the weak features, especially when one deals with very shallow features. Hundreds of prospectively observed weak unidentified features can give us an important insight into the nature of interstellar clouds, especially their apparently very complicated chemistry.