Intelligent interpretation of the astronomical UIE bands: the spectra similarity

Abstract

The limitations of visual inspection and interpretation of Infrared (IR) spectra from either laboratories or astronomical observations to cover a wide range of molecular types motivated us to apply a mathematical approach via a matching method called spectra similarity to identify the carriers of UIE bands in a sample of astronomical objects. The reliability of such a purely mathematical approach in targeting the correct molecular structures was tested by applying two sets of experimental IR spectra against the large pool of theoretical IR databases composed of 300,000 organic, organometallic, and, inorganic molecules. Spectra similarity calculations show that the second-row elements C, H, N, and O dominate the elemental composition of HD 44179, M 82, NGC 7023, NGC 7027, and Orion bar. In addition, the signatures of third-row elements S and Si were also identified. Our preliminary results confirm the signatures of complex organic molecules in interstellar environments. These are composed of benzene rings, five-membered rings, and side chain aliphatic groups in the cited astronomical sources. In some cases, the similarity approach suggested the fully aliphatic structures as the origin of UIE carriers.

Keywords:

• ISM
• spectra similarity
• IR spectra
• UIE bands
• UIE carriers

Acknowledgments

We are grateful to Professor Sun Kwok, Chair Professor at the University of Hong Kong, comments and edits on different parts of this manuscript and specially for the section on the organic molecules in solar system. We are also grateful for the support of Professor Quentin Andrew Parker, current Director of the Laboratory for Space Research, The University of Hong Kong. Chih Hao Hsia thanks Professor Quentin Andrew Parker and the University of Hong Kong for provision of his research post.

Author contributions

Seyed Adolreza Sadjadi: All theoretical computations and writing the manuscript. Chih Hao Hsia: Providing astronomically observed IR emission data, data reduction and writing the manuscript. Firman Ma: High school junior research assistant, organizing tables, corrections and proof reading. Silky Ma: High school junior research assistant, organizing figures, corrections and proof reading. Sadjadi and Hsia recognized the perseverance, hard work, and devotion to the science of these two young junior research assistants and therefore welcomed them to the co-authorship of the present work.

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Notes

1 The similarity software and the SIRD database are all part of Spartan 16 computational quantum chemistry package, PC version 2.0.7, parallel professional edition, running under Windows operating system^[47].

Additional information

Funding

SA. Sadjadi gratefully acknowledges Hong Kong, Small project funding from University of Hong Kong No. 201309176004, and the computing facilities offered by Information and Technology Services, University of Hong Kong.