The following document lists the file abstract/SSANDFOR_PAHS.abs
from catalogue VI/111.
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We propose to study the molecular symmetries of aromatic molecules in the interstellar medium and determine how these symmetries change as interstellar carbon evolves from the free molecular phase to incorporation into dust particles. These symmetries will be determined by searching for the characteristic infrared emission features produced by the C-H bending mode vibrations of specific polycyclic aromatic hydrocarbon (PAH) molecules and various forms of amorphous carbon in carbon-rich objects which span the evolutionary range from late carbon stars to molecular clouds. We propose to achieve this goal by measuring the 10.7-15.4 micron spectra of these objects. This spectral range spans the region where almost all PAH C-H out-of-plane bending modes fall. We have carried out laboratory studies that show that the positions of these bands are extremely sensitive to the molecular symmetry of the PAH and therefore promise to provide one of the best means for identifying specific PAHs in the interstellar medium. Identifying specific PAHs in the overall population and determining how this population evolves in time will provide direct insight into the chemical processes that affect PAHs and the physical processes associated with dust nucleation and growth in circumstellar shells and the interstellar medium. We propose to obtain spectra with ISO of sufficient quality to detect the many additional emission features which must be present longward of the well known 11.3 micron emission feature already observed from these objects. With our lab data we will be able to interpret these spectra in terms of which specific PAH molecules and amorphous carbon structures are present in these objects and determine their abundances. With data of the quality expected from ISO, it will finally be possible to probe directly into the process of carbon nucleation and growth, gaining insight into the evolution of carbon from its molecular form to larger amorphous particles, and understand which molecular species are associated with each type of object.