Laboratory spectra have revealed a wealth of molecular spectral
features in the wavelength range 20 - 180 microns which may
provide information on the physical processes taking place in
astrophysical objects especially those in which interactions
between gas and grains is important for the global chemical
evolution of these objects.
Among these features,far infrared H2O ice features at 45, 62
and 165 microns constitute an ideal target for ISO.
ISO provides a unique opportunity to investigate the long
wavelength continuum of cool emission from molecular clouds
surrounding Ultracompact HII regions and thus to determine the
nature of the grain components.
We propose to use LWS and SWS to obtain IR spectra in the 20
-180 microns domain of selected UC HII regions, predominantly
those with strong methanol emission at 6.668 GHz. These
spectra will provide information on the far IR opacity law
and the nature and structure of water ice, possibly mixed
with solid state contaminants such as O2, NH3, CH3OH, N2, in
the molecular clouds surrounding the sources. The far IR
spectral results will be compared with our own laboratory
spectra of analogues of these materials. They will be also
correlated with ground based observations of methanol maser
emission at 6.668 GHz and continuum emission at 8.4 GHz, near
IR images in the 1-3.6 microns region and near and mid IR
(10 microns) spectroscopy. Radiative transfer modelling will
be carried out and, with the knowledge of the physical state
of the ice (amorphous or crystalline) as determined with ISO
data, an evaluation of grain temperatures will be possible.