## Files in this item

FilesDescriptionFormat

application/pdf

1859.pdf (20kB)
AbstractPDF

## Description

 Title: Light on the 3 μm emission band from space with molecular beam spectroscopy Author(s): Maltseva, Elena Contributor(s): Buma, Wybren Jan; Lee, Timothy; Huang, Xinchuan; Oomens, Jos; Tielens, Xander; Petrignani, Annemieke; Candian, Alessandra; Mackie, Cameron J. Subject(s): Astronomy Abstract: The majority of interstellar objects shows IR emission features also known as unidentified infrared (UIR) emission bands. These UIR bands are attributed to IR emission of highly-excited gaseous polycyclic aromatic hydrocarbons (PAHs). To understand the physical conditions and chemical evolution of the interstellar environment a precise identification of the emission carriers is desired. The 3 $\mu$m UIR feature is represented by a strong band at 3040 cm$^{-1}$, a plateau from 3150 to 2700 cm$^{-1}$ and a number of weak features within this plateau. The 3040 cm$^{-1}$ component is assigned to fundamental CH-stretch vibrations of PAHs, but there still remain many questions on the origin of the other features. In this work we have studied experimentally the 3 $\mu$m region of regular, hydrogenated and methylated PAHs (up to 5 rings), combining molecular beam techniques with IR-UV ion dip spectroscopy, and theoretically by density functional theory (DFT) calculations within the harmonic and anharmonic approximation. We find that (a) the 3 $\mu$m region of PAHs is dominated by Fermi resonances and thereby cannot be treated within the harmonic approximation(b) the periphery structure of the molecules strongly affects the shape of the 3 $\mu$m band. In particular, the two-component emission interpretation can be explained by the presence of molecules with and without bay-hydrogens(c) due to strong Fermi resonances of fundamental modes with combination bands regular PAHs can significantly contribute to the 3 $\mu$m plateau in the 3150-2950 cm$^{-1}$, while hydrogenated and methylated species are primarily responsible for features in the 2950-2750 cm$^{-1}$ region. Issue Date: 2016-06-23 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91298 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2016-08-22
﻿