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  • Oxford University Press  (3)
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  • 1
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    Theoretical study of deuteronated PAHs as carriers for IR emission features in the ISM (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-21
    Description: This work proposes deuteronated PAH (DPAH + ) molecules as a potential carrier of the 4.4 and 4.65 μm mid-infrared emission bands that have been observationally detected towards the Orion and M17 regions. Density Functional Theory calculations have been carried out on DPAH + molecules to see the variations in the spectral behaviour from that of a pure polycyclic aromatic hydrocarbon (PAH). DPAH + molecules show features that arise due to the stretching of the aliphatic C–D bond. Deuterated PAHs have been previously reported as carriers for such features. However, preferred conditions of ionization of PAHs in the interstellar medium (ISM) indicates the possibility of the formation of DPAH + molecules. Comparison of band positions of DPAH + s shows reasonable agreement with the observations. We report the effect of size of the DPAH + molecules on band positions and intensities. This study also reports a D/H ratio ([D/H] $\rm _{sc}$ ; the ratio of C–D stretch and C–H stretch bands per [D/H] $\rm _{num}$ ) that is decreasing with the increasing size of DPAH + s. It is noted that large DPAH + molecules (no. of C atoms ~50) match the D/H ratio that has been estimated from observations. This ratio offers prospects to study the deuterium abundance and depletion in the ISM.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Theoretical study of deuteronated PAHs as carriers for IR emission features in the ISM (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-23
    Description: This work proposes deuteronated PAH (DPAH + ) molecules as a potential carrier of the 4.4 and 4.65 μm mid-infrared emission bands that have been observationally detected towards the Orion and M17 regions. Density Functional Theory calculations have been carried out on DPAH + molecules to see the variations in the spectral behaviour from that of a pure polycyclic aromatic hydrocarbon (PAH). DPAH + molecules show features that arise due to the stretching of the aliphatic C–D bond. Deuterated PAHs have been previously reported as carriers for such features. However, preferred conditions of ionization of PAHs in the interstellar medium (ISM) indicates the possibility of the formation of DPAH + molecules. Comparison of band positions of DPAH + s shows reasonable agreement with the observations. We report the effect of size of the DPAH + molecules on band positions and intensities. This study also reports a D/H ratio ([D/H] $\rm _{sc}$ ; the ratio of C–D stretch and C–H stretch bands per [D/H] $\rm _{num}$ ) that is decreasing with the increasing size of DPAH + s. It is noted that large DPAH + molecules (no. of C atoms ~50) match the D/H ratio that has been estimated from observations. This ratio offers prospects to study the deuterium abundance and depletion in the ISM.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
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    PAPER CURRENT
  • 3
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    The 11.2 {mu}m emission of PAHs in astrophysical objects (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-10
    Description: The 11.2-μm emission band belongs to the family of the ‘unidentified’ infrared emission bands seen in many astronomical environments. In this work, we present a theoretical interpretation of the band characteristics and profile variation for a number of astrophysical sources in which the carriers are subject to a range of physical conditions. The results of Density Functional Theory calculations for the solo out-of-plane vibrational bending modes of large polycyclic aromatic hydrocarbon (PAH) molecules are used as input for a detailed emission model which includes the temperature and mass dependence of PAH band wavelength, and a PAH mass distribution that varies with object. Comparison of the model with astronomical spectra indicates that the 11.2-μm band asymmetry and profile variation can be explained principally in terms of the mass distribution of neutral PAHs with a small contribution from anharmonic effects.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
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    PAPER CURRENT
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