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We report the first spectroscopic observations of a background star seenthrough the region between the ionization front and the dissociation front ofthe nebula IC 63. This photodissociation region (PDR) exhibits intense extendedred emission (ERE) attributed to fluorescence by large molecules/ions. Wedetected strong diffuse interstellar bands (DIB) in the stellar spectrum,including an exceptionally strong and broad DIB at $\lambda$4428. The detectionof strong DIBs in association with ERE could be consistent with the suggestionthat the carriers of DIBs and ERE are identical. The likely ERE process isrecurrent fluorescence, enabled by inverse internal conversions from highlyexcited vibrational levels of the ground state to low-lying electronic stateswith subsequent transitions to ground. This provides a path to rapid radiativecooling for molecules/molecular ions, greatly enhancing their ability tosurvive in a strongly irradiated environment. The ratio of the equivalentwidths (EW) of DIBs $\lambda$5797 and $\lambda$5780 in IC 63 is the same asthat observed in the low-density interstellar medium with UV interstellarradiation fields (ISRF) weaker by at least two orders of magnitude. Thisfalsifies suggestions that the ratio of these two DIBs can serve as a measureof the UV strength of the ISRF. Observations of the nebular spectrum of the PDRof IC 63 at locations immediately adjacent to where DIBs were detected failedto reveal any presence of sharp emission features seen in the spectrum of theRed Rectangle nebula. This casts doubts upon proposals that the carriers ofthese features are the same as those of DIBs seen at slightly shorterwavelengths.

Are the Carriers of Diffuse Interstellar Bands and Extended Red Emission the same?