Reflection nebulae (RNs) are objects of SPECIAL INTEREST because
 they provide an opportunity to explore the interaction of a single
 star with a region of high density ISM.They are bright enough to permit
 a detailed spectroscopy of the emission by IS dust and gas .

  In addition, the characteristics of the stellar radiation
 incident can vary from object to object (O/B to M stars), allowing
 tests of specific models for the excitation of different IS species.
 Our proposal will use ISO to study a sample of RNs illuminated with
 widely varying temperatures.

  We propose to obtain:
 - complete 2.5-200 um spectra for a subset of RNs with varying stellar
 temperature. This is the HEART OF THE  PROPOSAL.
 - 3-200 um broad band energy distributions of the emission for all RNs.
 - measurement of the gas heating efficiency for a subset of RNs, by
 varying(i) the IRRADIATION SPECTRA (O/B to M stars) and (ii)
 the FLUX INTENSITY (different distances from the star in a given RN).

  Specifically, we want to:
 - confirm or deny the PAH hypothesis;if confirmed, make a more specific
 identification of the molecular species and correlate their ionization
 and dehydrogenation states with the stellar irradiation.
 - search for C60 molecules or ions.
 - look for spectral features that could identify the particles emitting
 by temperature fluctuations in the 20-100 um range, because, presently,
 we know NOTHING on their chemical nature.
 - determine whether there is a cut-off in the exciting star temperature
 underwhich the gas heating efficiency drops, as expected if the heating
 mechanism is photoelectric effect.