The CH out of plane bending modes of PAH molecules in astrophysical environments

By S. Hony, C. V. Kerckhoven, E. Peeters, A. Tielens, D. Hudgins, L. Allamandola. 2001

301 citations recorded by the source corpus.

We present 10 15 m spectra of as ample of Hii regions, YSOs and evolved stars that show strong unidentied infrared emission features, obtained with the ISO/SWS spectrograph on-board ISO. These spectra reveal a plethora of emission features with bands at 11.0, 11.2, 12.0, 12.7, 13.5 and 14.2 m. These features are observed to vary considerably in relative strength to each-other from source to source. In particular, the 10{15m spectra of the evolved stars are dominated by the 11.2 m band while for H ii regions the 12.7 is typically as strong as the 11.2 m band. Analysing the ISO data we nd a good correlation between the 11.2 mb and and the 3.3 m band, and between the 12.7 ma nd the 6.2m band. There is also a correlation between the ratio of the UIR bands to the total dust emission and the 12.7 over 11.2 m ratio. Bands in the 10{15 ms pectral region are due to CH out of plane (OOP) bending modes of polycyclic aromatic hydrocarbons (PAHs). We summarise existing laboratory data and theoretical quantum chemical calculations of these modes for neutral and cationic PAHs. Due to mode coupling, the exact peak position of these bands depends on the number of adjacent CH groups and hence the observed interstellar 10 15 m spectra can be used to determine the molecular structure of the interstellar PAHs emitting in the dierent regions. We conclude that evolved stars predominantly inject compact 100 200 C-atom PAHs into the ISM where they are subsequently processed, resulting in more open and uneven PAH structures.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/a2714774c9cf0d3c186a14c9526f0b64e4671c2b

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Citations in the corpus

Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation? (2004, methodology): “…importance here are the studies of the PAHs in H ii regions, which characterized the UIR bands (and their variations) in massive star-forming regions (Verstraete et al. 1996, 2001; Van Kerckhoven et al. 2000; Hony et al. 2001; Peeters et al. 2002a; Vermeij et al. 2002; van Diedenhoven et al. 2004).”
Stellar Evolutionary Effects on the Abundances of Polycyclic Aromatic Hydrocarbons and Supernova-Condensed Dust in Galaxies (2007, background): “However, PAHs are abundantly observed during the later planetary nebula phase (Hony et al. 2001).”
The Profiles of the 3-12 Micron Polycyclic Aromatic Hydrocarbon Features (2004, background): “Lastly, the 3.3 and 11.2 bands are well correlated and behave differently then the 6.2 and 7.7 bands that are dominated by PAH cations (Hony et al. 2001).”
ISO spectroscopy of disks around Herbig Ae/Be stars , (2004, background): “Dehydrogenation of PAHs, when the molecules are stripped of their H atoms, is believed not to play a crucial role (Hony et al. 2001).”
High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies (2007, background): “Large molecules give rise to several emission and absorption features; the most prominent emission features are seen from 3.3 to about 19 m and arise from bending and stretching modes of polycyclic aromatic hydrocarbons (Puget & Leger1989; Hony et al. 2001).”
The rich 6 to 9 vec mu m spectrum of interstellar PAHs (2002, methodology): “These variations stand in marked contrast to the behaviour of 3.3 and 11.2 µm bands whose profiles and peak positions are quite invariable (Hony et al. 2001, Peeters et al. 2002, in prep.”
ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks (2004, background): “Whereas the CH 3.3 and 11.2 µm bands correlate well with each other over a wide range of conditions, significant variations in the relative strengths of the C-H and C-C features are found, both between different types of sources and at different positions within a source (e.g., Hony et al. 2001).”
Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population (2005, background): “…detailed positions, profiles, and relative intensities of the interstellar emission bands—variations that correlate with object type and radiation environment (Hony et al. 2001; Peeters et al. 2002) and with spatial structure within extended objects (Sloan et al. 1997, 1999; Bregman & Temi 2005).”
The Mid-Infrared Spectrum of Star-forming Galaxies: Global Properties of Polycyclic Aromatic Hydrocarbon Emission (2006, background): “Evidence in our own Galaxy (e.g. Joblin et al. 1996; Verstraete et al. 1996; Hony et al. 2001; Peeters et al. 2004; Bregman & Temi 2005) and resolved regions in nearby galaxies like the LMC and SMC (Contursi et al. 2000; Vermeij et al. 2002), indicate that the PAH emission spectrum is variable on…”
SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, background): “Thus, the strong suppression of the 6.2 or 7.7 µm complex observed in galaxies that host low-luminosity AGN (Sturm et al. 2006; Smith et al. 2007) and in some star-forming regions (Hony et al. 2001) does not occur in ULIRGs.”
Laboratory Infrared Spectroscopy of Cationic Polycyclic Aromatic Hydrocarbon Molecules (2003, background): “…galactic nuclei, and starburst galaxies (Verstraete et al. 1996, 2001; Moutou et al. 1999; Joblin et al. 2000; Genzel et al. 1998; Henning et al. 1998; Boulanger et al. 1998; Mattila et al. 1996; Mattila, Lehtinen, & Lemke 1999; van Kerckhoven et al. 2000; Hony et al. 2001; Peeters et al. 2002).”
The origin of crystalline silicates in the Herbig Be star HD 100546 and in comet Hale-Bopp (2003, background): “Apart from the bands at 6.25, 7.9 and 11.3µm, also PAH features at longer wavelengths can be observed (see also Hony et al. 2001).”
The Infrared Spectra of Very Large, Compact, Highly Symmetric, Polycyclic Aromatic Hydrocarbons (PAHs) (2008, methodology): “…trio hydrogens deduced with respect to solo and duo hydrogens on the emitting astronomical PAH population must be reduced, in some cases, by as much as a factor of 2, implying that the PAH structures Hony et al. (2001) previously deduced should be modified to favor more compact and symmetric forms.”
The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy (2006, background): “The PAH features at 14.2 m (Hony et al. 2001) and 17 m (Van Kerckhoven et al. 2000) are intrinsically weaker but are located in spectrally less complex regions, allowing a different approach.”
Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium (2000, unknown): “Thus one expects a much lower quartet-CH (13.6 km) abundance than solo-, duet-, and trio-CH for interstellar PAHs, as has been conÐrmed recently by ISO observations (Hony et al. 2001).”
THE INFRARED SPECTRA OF VERY LARGE IRREGULAR POLYCYCLIC AROMATIC HYDROCARBONS (PAHs): OBSERVATIONAL PROBES OF ASTRONOMICAL PAH GEOMETRY, SIZE, AND CHARGE (2009, methodology): “Thus the ratios of different edge groups presented in Table 4 of Hony et al. (2001) should be halved.”