Resolved profiles of diffuse interstellar bands: Evidence for rotational contours of gas-phase molecules

From high resolution and high signal to noise spectra, we resolved two or three peak substructures and wing asymmetries in the spectral profiles of three narrow diffuse interstellar bands (DIBs). The measured profiles show specific similarities with calculated rotational contours of gas phase molecular spectra, confirming the theory that gas phase molecules are some of the DIB carriers. We measured small changes of the profile substructures with the interstellar line of sight gas temperature. Minor changes in the DIB widths and wings indicate a limited geometry distortion of the molecule in the excited state. By comparison with model calculations of polycyclic aromatic hydrocarbons (PAHs) and fullerenes, our observations indicate that the molecular carriers of the DIBs at 5797, 6379 and 6613 Å have rotational constants smaller than 0.004 cm^-1, and would correspond to large PAH molecules with more than 40 C atoms, chains of ∼ 12-18 C atoms, 30 C rings or C₆₀ fullerene compounds.