Current assessment of the Red Rectangle band problem
  In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition, and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions are made for future studies to enhance our understanding of these enigmatic bands. 
R. J. Glinski, P. D. Michaels, C. M. Anderson, T. W. Schmidt, R. G.   Sharp, M. L. Sitko, L. S. Bernstein, and H. Van Winckel
astro-ph.GA