Diffuse interstellar bands: resolved rotational band structure at 5850A.

The only candidate of what may be a resolved rotational vibrational band in the DIB Survey of Jenniskens & Desert (1994), the triplet of bands at 5844, 5850 and 5852 A, is examined in detail in order to establish the nature of these DIBs. We find that superposed on the broad λ5844 are four weak features, reminiscent of substructure found on top of the broad λ5778. The relative band strength of DIBs λ5844 and λ5850 correlates with the rotational temperature in the J=0 and J=1 levels of molecular hydrogen. However, we do not find variations in band shape that are consistent with substructure of a resolved rotational band profile. Instead, the narrow λ5850 is found to have a shoulder on the red and blue side of the main band, which can imply that this band itself is an unresolved rovib band with P, Q and R branches.