Abstract Details

Conference ID: ASI2017_708
Title : The Deuterium abundance in astrophysical PAHs
Authors and Co-Authors : M. Buragohain(1), P.J. Sarre(2), T. Onaka3, I. Sakon(3) 1-Department of Physics, Tezpur University, Tezpur 784 028, India 2-School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK 3-Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
Abstract Type : Oral
Abstract Category : Stars,ISM and the Galaxy
Abstract : The presence of polycyclic aromatic hydrocarbon (PAH) molecules in the interstellar medium (ISM) of the Milky Way and external galaxies is confirmed by the observation of emission features at 3.3, 6.2, 7.7, 8.6 and 11.2 µm popularly known as the aromatic infrared bands (AIBs) (Tielens et al. 2008). Astronomers suggest that about 10% - 15% of the interstellar carbon budget is within PAHs. Apart from the pure PAHs, substituted PAHs play an important role in interstellar chemistry. PAHs might host significant fraction of elements other than carbon and hydrogen. Deuterium is an important interstellar component that may be added to PAHs by direct association or by replacing one of the H atom. ISO observations show that C – D stretching in deuterated PAHs (PADs) gives rise to the 4.4 and 4.65 µm features (Peeters et al. 2004). Further, PADs have also been incorporated in a deuterium depletion model to account for the missing Deuterium (Draine 2006). AKARI observations do show similar features but suggest a smaller fraction of deuterium within PAHs (Onaka et al. 2014) . We present theoretical infrared spectra of deuterated and deuteronated interstellar PAHs (DPAH+) (Buragohain et al. 2015, Buragohain et al. 2016). A deuteronated PAH (DPAH+) is a PAH with one deuteron (D+) added. The site where the D+ is added becomes aliphatic in nature. We discuss the D/H ratio and compare it to the observation estimates. A detailed analysis of the IR spectra of these molecules is presented and discussed in context of possible astrophysical implications. Possible mechanisms for the formation of deuteronated PAHs are also discussed.