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Title: On the Origin of the 3.3 μ m Unidentified Infrared Emission Feature

Abstract

The 3.3 μ m unidentified infrared emission feature is commonly attributed to the C–H stretching band of aromatic molecules. Astronomical observations have shown that this feature is composed of two separate bands at 3.28 and 3.30 μ m, and the origin of these two bands is unclear. In this paper, we perform vibrational analyses based on quantum mechanical calculations of 153 organic molecules, including both pure aromatic molecules and molecules with mixed aromatic/olefinic/aliphatic hydridizations. We find that many of the C–H stretching vibrational modes in polycyclic aromatic hydrocarbon (PAH) molecules are coupled. Even considering the uncoupled modes only, the correlation between the band intensity ratios and the structure of the PAH molecule is not observed, and the 3.28 and 3.30 μ m features cannot be directly interpreted in the PAH model. Based on these results, the possible aromatic, olefinic, and aliphatic origins of the 3.3 μ m feature are discussed. We suggest that the 3.28 μ m feature is assigned to aromatic C–H stretch whereas the 3.30 μ m feature is olefinic. From the ratio of these two features, the relative olefinic to aromatic content of the carrier can be determined.

Authors:
; ;  [1]
  1. Laboratory for Space Research, Faculty of Science, The University of Hong Kong, Pokfulam Road, Hong Kong (China)
Publication Date:
OSTI Identifier:
22663219
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 845; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRELATIONS; EMISSION; INTERSTELLAR SPACE; MOLECULES; POLYCYCLIC AROMATIC HYDROCARBONS; QUANTUM MECHANICS

Citation Formats

Sadjadi, Seyedabdolreza, Zhang, Yong, and Kwok, Sun, E-mail: sunkwok@hku.hk. On the Origin of the 3.3 μ m Unidentified Infrared Emission Feature. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA8141.
Sadjadi, Seyedabdolreza, Zhang, Yong, & Kwok, Sun, E-mail: sunkwok@hku.hk. On the Origin of the 3.3 μ m Unidentified Infrared Emission Feature. United States. doi:10.3847/1538-4357/AA8141.
Sadjadi, Seyedabdolreza, Zhang, Yong, and Kwok, Sun, E-mail: sunkwok@hku.hk. Sun . "On the Origin of the 3.3 μ m Unidentified Infrared Emission Feature". United States. doi:10.3847/1538-4357/AA8141.
@article{osti_22663219,
title = {On the Origin of the 3.3 μ m Unidentified Infrared Emission Feature},
author = {Sadjadi, Seyedabdolreza and Zhang, Yong and Kwok, Sun, E-mail: sunkwok@hku.hk},
abstractNote = {The 3.3 μ m unidentified infrared emission feature is commonly attributed to the C–H stretching band of aromatic molecules. Astronomical observations have shown that this feature is composed of two separate bands at 3.28 and 3.30 μ m, and the origin of these two bands is unclear. In this paper, we perform vibrational analyses based on quantum mechanical calculations of 153 organic molecules, including both pure aromatic molecules and molecules with mixed aromatic/olefinic/aliphatic hydridizations. We find that many of the C–H stretching vibrational modes in polycyclic aromatic hydrocarbon (PAH) molecules are coupled. Even considering the uncoupled modes only, the correlation between the band intensity ratios and the structure of the PAH molecule is not observed, and the 3.28 and 3.30 μ m features cannot be directly interpreted in the PAH model. Based on these results, the possible aromatic, olefinic, and aliphatic origins of the 3.3 μ m feature are discussed. We suggest that the 3.28 μ m feature is assigned to aromatic C–H stretch whereas the 3.30 μ m feature is olefinic. From the ratio of these two features, the relative olefinic to aromatic content of the carrier can be determined.},
doi = {10.3847/1538-4357/AA8141},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 845,
place = {United States},
year = {2017},
month = {8}
}