Resolution of intrinsic fine structure in spectra of narrow diffuse interstellar bands

The first ultrahigh-resolution spectra of two of the stronger and narrower diffuse interstellar bands, at wavelengths of 5797 and 6614, have been recorded along lines of sight towards relatively lightly reddened stars with the Ultra-High-Resolution Facility on the 3.9-m Anglo-Australian Telescope. We have discovered that these bands are composed of partially resolved and wavelength-invariant components, which are most readily interpreted in terms of rotational branch structure associated with electronic transitions of gas-phase molecules. These new observational results add considerable weight to the attribution of the 5797 and 6614 wavelength diffuse bands to transitions in free molecules. (Author)