TENTATIVE IDENTIFICATION OF DIFFUSE INTERSTELLAR ABSORPTION BANDS AND OF A DIFFUSE INTERSTELLAR DOUBLET LINE

The four diffuse interstellar absorption bands at λ4430, λ4760, λ4890, and λ6180 and the two diffuse lines at λ5780 and λ5797 are interpreted as belonging to pre-ionization transitions in H- and O-, respectively. In both cases the identifications are supported by extrapolations of wave numbers of resonance lines along isoelectronic sequences. In the H- case the hypothesis as to the origin of the bands is supported by quantum-mechanical results by Herzenberg and Mandl (1963) as to the positions of resonances in collisions between neutral hydrogen atoms and free electrons. The relatively large intensities of the forbidden transitions indicate that the extent of the ion in its excited states may be very large as compared to ordinary atomic dimensions. In the O- case the relative doublet separation, as extrapolated along the isoelectronic sequence, is used for the identification of the doublet. © 1969 D. Reidel Publishing Company.