Are the Carriers of Diffuse Interstellar Bands and Extended Red Emission
  the same?
  We report the first spectroscopic observations of a background star seen
through the region between the ionization front and the dissociation front of
the nebula IC 63. This photodissociation region (PDR) exhibits intense extended
red emission (ERE) attributed to fluorescence by large molecules/ions. We
detected strong diffuse interstellar bands (DIB) in the stellar spectrum,
including an exceptionally strong and broad DIB at $\lambda$4428. The detection
of strong DIBs in association with ERE could be consistent with the suggestion
that the carriers of DIBs and ERE are identical. The likely ERE process is
recurrent fluorescence, enabled by inverse internal conversions from highly
excited vibrational levels of the ground state to low-lying electronic states
with subsequent transitions to ground. This provides a path to rapid radiative
cooling for molecules/molecular ions, greatly enhancing their ability to
survive in a strongly irradiated environment. The ratio of the equivalent
widths (EW) of DIBs $\lambda$5797 and $\lambda$5780 in IC 63 is the same as
that observed in the low-density interstellar medium with UV interstellar
radiation fields (ISRF) weaker by at least two orders of magnitude. This
falsifies suggestions that the ratio of these two DIBs can serve as a measure
of the UV strength of the ISRF. Observations of the nebular spectrum of the PDR
of IC 63 at locations immediately adjacent to where DIBs were detected failed
to reveal any presence of sharp emission features seen in the spectrum of the
Red Rectangle nebula. This casts doubts upon proposals that the carriers of
these features are the same as those of DIBs seen at slightly shorter
wavelengths.
