We report high-resolution (R ～ 37,000) integral field spectroscopy of the central region (r < 14″) of the Red Rectangle nebula surrounding HD 44179. The observations focus on the λ5800 emission feature, the bluest of the yellow/red emission bands in the Red Rectangle. We propose that the emission feature, widely believed to be a molecular emission band, is not a molecular rotation contour, but a vibrational contour caused by overlapping sequence bands from a molecule with an extended chromophore. We model the feature as arising in a polycyclic aromatic hydrocarbon (PAH) with 45-100 carbon atoms.
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