Role of PAHs and its derivatives in astrophysical Infrared emissions
Abstract
It is now well recognized that the vibrational transitions in polycyclic aromatic hydrocarbons (PAHs) give rise to the astrophysical infrared emission features at 3.3, 6.2, 7.7, 8.6, 11.2, 12.7 and 16.4 μm. Also the variations in the band profiles could be due the different types of PAHs in different environments. The possible molecules could be plain PAHs of varying size and shape or PAHs with side groups. The observed infrared emission features are complex composite resultant of the vibrational transitions within individual PAHs. Analysis of the infrared spectral properties of the possible PAHs and their correlation with the observed emission features give useful insight into the source physical and chemical environment. It is therefore important to have infrared spectral information of a large set of different types of PAHs. Synthesis and laboratory study of all possible PAHs is difficult. Quantum chemical calculations are useful in this regard and provide the needed information. The chemical calculations are restricted by the choice of basis sets and scaling procedure. The use of suitable basis set and modelling of combination spectra shall be discussed. Matching of all the observed bands simultaneously require considering PAHs with vinyl or acetylenic side groups. For very large PAHs the lattice skeletal vibrations could also give rise to features in the far-infrared. Some important common features and their correlation with observations will also be presented.
- Publication:
-
39th COSPAR Scientific Assembly
- Pub Date:
- July 2012
- Bibcode:
- 2012cosp...39.1580R