VARIATIONS OF THE 8.6 AND 11.3 MU-M EMISSION BANDS WITHIN NGC-1333 - EVIDENCE FOR POLYCYCLIC AROMATIC HYDROCARBON CATIONS

We have obtained 8-13 mu m spectra of three positions in the IR reflec tion nebula associated with SVS 3 in NGC 1333. These observations reve al systematic variations in the relative intensities of the IR emissio n features at 8.6 mu m and 11.3 mu m. In particular, the [8.6]/[11.3] ratio is highest at the position of the exciting star and decreases wi th increasing angular distance from the star. We attribute these varia tions to changes in the relative populations of ionized and neutral po lycyclic aromatic hydrocarbons (PAHs), driven by the strong far-ultrav iolet radiation field near the star. From experiments and quantum chem ical theoretical studies, the intrinsic strength of these two bands is known to vary with the charge state of the emitting PAH. We have deve loped a simple model for the relative intensity of the 8.6 and 11.3 mu m bands taking the charge state of the carrier into account. This mod el is in good agreement with the data. We point out several observatio nal and experimental tests of this model.