LINE-PROFILES OF DIFFUSE INTERSTELLAR LINES AT 5780A, 5797A

Photoelectric coude scanner observations of the interstellar diffuse lines at 5780 and 5797 Å are reported. With a resolution of about 0.2 Å, line profile differences are seen in the sample of eight stars. In part, these are attributed to the overlapping contributions from the several clouds in the line of sight. Intrinsic profile differences are also suggested. The hypothesis that some of the diffuse lines represent electronic transitions in large molecules is examined. Synthetic spectra are shown which approximate the observed profiles. Excitation of these hypothetical molecules is examined. Their stability against photodissociation by the interstellar ultraviolet radiation field is noted as a key problem for future study. © Royal Astronomical Society.