| Abstract : | Single or fused Benzene rings constitute aromatics that are highly stable due to the presence of delocalized electrons. These molecules are ubiquitous in terrestrial environments and are formed by the burning of hydrocarbons (viz. vehicle exhausts, smokes, etc.). We focus on aromatics, specifically Polycycylic Aromatic Hydrocarbon (PAH) molecules that are expected to be present in interstellar space and are inherently involved with the chemistry of the local environment.
The presence of PAH molecules is known by the observation of strong emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 µm in the Milky Way and in external galaxies. Confirmation of the presence of fullerene cation in the interstellar medium (ISM) strongly supports the presence of PAHs. In the harsh interstellar conditions, PAHs experience physical and chemical processing that brings changes in the molecule. Ionization, dehydrogenation, etc. produce significant spectral signatures that are being diagnosed spectroscopically.
We have been studying variants of PAHs, viz., deuterated, dehydrogenated and also with addition of aliphatic side groups. Density functional theory (DFT) has been used to calculate the theoretical vibrational spectra of PAHs. The spectra obtained matches well with available experimental spectra and provides important clues to the form of PAHs present in the ISM. We also present rotational spectra of nitrogen containing PAHs that may help in detection of these PAHs.
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