E. Peeters 1 A.G.G.M. Tielens 2 P.R. Roelfsema 1 P. Cox 3
1 SRON-Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
2 Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands
3 Institut d'Astrophysique Spatiale, Bât.120, Université de Paris XI, 91405 Orsay, France
As part of the ISO guaranteed time program devoted to the study of
compact H II regions in the Galaxy, ISO-SWS spectra covering the
whole SWS wavelength range from a large sample of H II regions were
obtained. The sample covers a large range in galactic radii from the
galactic center out to a distance of 
25 kpc.
In addition to strong atomic emission lines, these data show a wealth of
infrared emission features attributed to Polycyclic Aromatic
Hydrocarbons (PAHs). The strength and shape of these features exhibit
considerable variations in different lines-of-sight. These varations are
thought to be primarily due to variations in the physical conditions of
the emitting region (radiation field, density etc.).
The first results of a study on the properties of PAHs under different physical conditions will be presented. Typical source spectra will be shown for the various observed PAH spectral shapes. The influence of the environment on the observed PAH features and the variations across the galaxy of PAH abundances and their physical properties will be discussed.