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

Abstract

The first ultra-high-resolution spectra of two of the stronger and narrower diffuse interstellar bands, λλ5797 and 6614, have been recorded along lines of sight towards relatively lightly reddened stars with the Ultra-High-Resolution Facility (UHRF) 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 λλ5797 and 6614 diffuse bands to transitions in free molecules.