| Description |
Strong emission features at 3.3, 6.2, 7.7, and 11.2 um dominate the mid-infrared spectra of most interstellar objects. These IR features are due to vibrational fluorescence of large (50-150 C-atom) Polycyclic Aromatic Hydrocarbon molecules pumped by UV photons. These species will also have bands at far-infrared wavelength, notably due to .drum-head modes. We have performed experimental and theoretical studies that demonstrate that these bands carry unique information, particularly on the size of the emitting species that cannot be obtained from the shorter wavelength bands. We propose to measure the far-IR spectra of a sample of well-studied PAH sources using PACS and SPIRE. The sample has been carefully selected to show strong mid-IR PAH bands, and a relatively weak dust continuum at the Herschel wavelengths to maximize the line-to-continuum ratio for far-IR PAH bands. These observations are designed to measure infrared bands to a level of 1% of the dust continuum. Together with the Spitzer/ISO studies, the full spectrum of the IR emission features from 3 to 600 um can be determined. In order to determine the implications for the emitting PAHs, we will compare these bands to the PAH database that we have compiled over the last 15 years and analyze the emission using the realistic PAH emission model that we have developed over the years. |
