Abstract Details
| Name: MRIDUSMITA BURAGOHAIN Affiliation: TEZPUR UNIVERSITY Conference ID: ASI2016_636 Title : Vibrational spectra of deuterated PAHs: C-H out-of-plane vibrations Authors and Co-Authors : Amit Pathak, Department of Physics Peter Sarre, The University of Nottingham Abstract Type : Poster Abstract Category : Stars, The Milky Way Galaxy and its neighbours Abstract : Mid-infrared emission lines popularly known as 'Aromatic Infrared Bands' are one of the most commonly observed features in the interstellar medium (ISM). Since its fist discovery in 1973, these bands have frequently been detected towards a diverse astrophysical source indicating its widespread presence in the ISM (Tielens 2008). Observations show prominent emissions lines at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 µm in the AIB spectrum whereas several minor bands are identified recently in the 3-20 µm regions. Three decades ago, Léger and Puget proposed Polycyclic Aromatic Hydrocarbon (PAH) molecules responsible for producing such emission lines in the ISM (Léger and Puget 1984). PAH molecules show IR spectra that are consistent with characteristic frequencies of the AIBs. According to the PAH-AIB hypothesis, an interstellar PAH molecule illuminates in IR due to the vibrational relaxation after absorbing a background UV photon (Allamandola et al. 1989). Despite the wide acceptance of the PAH-AIB hypothesis, identification of exact form of PAH molecules still faces major challenges. Extensive studies on PAHs, both laboratory and theoretical present a wide range of interstellar PAH family that strongly account for some of the observed bands, if not all. A recent study proposes PAH molecules with deuterium content (PADs) as AIB carrier that may explain the observed features in the 4-5 µm regions (Peeters et al. 2004). 11.2 µm features is one of the most distinctive band in the AIB spectrum and has been assigned to the C-H out of plane (OOP) bending mode in a neutal PAH that contains a solo C-H group (Hudgins & Allamandola 1999). This work reports a Density Functional Theory (DFT) study on PAH molecules with a solo C-D group to study the vibrational modes present in such molecules and to see the effect of deuteration on the 11.2 micron feature. DFT calculation has also been carried out for PAH molecules with duet, trio and quartet C-D groups to see the variations in the IR spectra. We present a detailed analysis of the IR spectra of these molecules and discuss the possible astrophysical implications. References: 1. Tielens, A. G. G. M., 2008, ARA&A, 46, 289. 2. L´eger, A. & Puget, J. L., 1984, A&A, 137, L5. 3. Allamandola, L. J., Tielens, A. G. G. M., & Barker, J. R., 1989, ApJS, 71, 733. 4. Peeters, E., Allamandola, L. J., Bauschlicher, Jr., C. W., Hudgins, D. M., Sandford, S. A., & Tielens, A. G. G. M., 2004, ApJ, 604, 252. 5. Hudgins, D. M. & Allamandola, L. J., 1999, ApJ, 516, L14. |