Ultraviolet Photoprocessing of Interstellar Dust Mantles as a Source of Polycyclic Aromatic Hydrocarbons and Other Conjugated Molecules

Greenberg, J. Mayo; Gillette, Jarred; Muñoz, G. M.; Mahajan, Tania B.; Zare, Richard N.; Li, Aigen; Schütte, W. A.; Groot, M. de; Mendoza-Gomez, C. X.

doi:10.1086/312526

Cited by 74 publications

(40 citation statements)

References 29 publications

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“…The observation of vinylacetylene in the ice potentially yields a formation pathway towards PAHs to which it is known to be a precursor. This is an interesting finding, because PAHs are ubiquitous in space, and they are generally assumed to form in the outflows of AGB stars, in accordance with the experiments of Greenberg et al (2000) that analyze gas chromatographically residues obtained after UV photolysis of ice and ice residu. The present results hint at a (complementary) bottom-up formation mechanism..…”

Section: Astrophysical Implicationssupporting

confidence: 79%

Vacuum ultraviolet photochemistry of solid acetylene: a multispectral approach

Cuylle

Zhao

Strazzulla

et al. 2014

A&A

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Aims. Gas phase acetylene (C 2 H 2 ) and polyynes (H(-C≡C-) m H) are ubiquitous in the interstellar medium. However, astrochemical models systematically underestimate the observed abundances, supporting the idea that enrichment from the solid state takes place. In this laboratory-based study, we investigate the role C 2 H 2 plays in interstellar ice chemistry and we discuss the way its photoproducts may affect gas phase compositions. Methods. C 2 H 2 ice is investigated under vacuum ultraviolet (VUV) irradiation in its pure form as present in the atmosphere of Titan and in a water-dominated ice as present on grain mantles in molecular clouds and on comets. To disentangle the photochemical network, a unique, complementary combination of infrared and ultraviolet-visible (UV-VIS) spectroscopy is used. Results. From the experimental results, it can be concluded that the VUV-induced solid state C 2 H 2 reaction network is dominated by polymerization resulting in the formation of polyynes at least up to C 20 H 2 and larger polyyne-like molecules. At low temperatures, this process takes place very efficiently and suggests low barriers. When extending this reaction scheme to a water-rich environment, the dominant reaction products are CO and CO 2 but the simultaneous detection of polyyne like molecules is evidence that the reactions as observed in pure C 2 H 2 ice persist. Conclusions. From the spectroscopic evidence as presented in this laboratory study, it is concluded that the formation of polyynes upon VUV irradiation of interstellar ices is a process that may contribute to at least part of the observed gas phase enrichment in space.

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Section: Astrophysical Implicationssupporting

confidence: 79%

Vacuum ultraviolet photochemistry of solid acetylene: a multispectral approach

Cuylle

Zhao

Strazzulla

et al. 2014

A&A

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“…7. Considering that PAHs are associated with the cold dust and thus molecular clouds, possible mechanisms for the enhanced PAH abundance are (1) the synthesis of PAHs in molecular clouds (Greenberg et al 2000), or (2) BG shattering and/or swept up into shells by slow shocks with velocities lower than ∼75 km s −1 (Jones et al 1996;Hunter et al 2006). Sandstrom et al (2010) found that the PAH abundance was correlated with cold dust and CO emission, and suggested the possibility of PAH formation in molecular clouds.…”

Section: Enhanced Star-forming Activity In Regions Around the Giant Smentioning

confidence: 99%

AKARI view of star formation in NGC 1313

Suzuki

Kaneda

Onaka

2013

A&A

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Context. In the southwest region of NGC 1313, patchy star-forming regions are found. In the neighborhood, is a giant supershell with a diameter of 3.2 kpc. However, the direct association between star-forming regions and the giant supershell is still unclear. Aims. We investigate the relation between the surface densities of the gas (Σ gas ) and star formation rate (Σ SFR ) within the disk of NGC 1313 to obtain the spatial distribution of the star formation efficiency (SFE). Methods. NGC 1313 was observed with the Infrared Camera (IRC) and Far-Infrared Surveyor (FIS) onboard AKARI in ten bands at 3. 2, 4.1, 7, 11, 15, 24, 65, 90, 140, and 160 μm. With these AKARI ten-band images, we spectrally decomposed the stellar and polycyclic aromatic hydrocarbon (PAHs) components in addition to the cold (∼20 K) and warm (∼60 K) dust emission components. The cold and warm dust components were converted into the gas mass and the SFR. Results. The SFE shows high values in the regions around the giant supershell, with the highest SFE in the galaxy in the southern spiral arm region. A similar trend can be seen in the spatial distribution of the PAH abundance relative to big grains. We find a powerlaw dependence of the star formation rate per unit area on the column density Σ SFR proportional to Σ N gas . From a region-by-region analysis, the power-law index N for the northern spiral arm is found to be N 2.0, which is observed on typical spiral arms, whereas those for the southern spiral arm and giant supershell regions have an index of N ∼ 1.6. Conclusions. The PAH abundance and the SFE show anomalously high values in regions around the giant supershell. The enhanced PAH abundance can be caused by shattering of big grains through slow shocks (40 km s −1 ). The power-law index N = 1.62 ± 0.06 obtained in the giant supershell region can be accounted for by the star formation scenario with collect-and-collapse in the expanding giant supershell. These pieces of evidence strongly indicate that the giant supershell has triggered the star formation and enhanced the SFE.

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“…Taking advantage of the selectivity and sensitivity of L 2 MS toward PAHs, we have investigated this process by characterizing nonvolatile aromatic photo-products in irradiated interstellar ice analogs (37)(38)(39)(40)(41). This work was performed in collaboration with the NASA Ames Research Center Astrochemistry group and researchers at the University of Leiden.…”

Section: Interplanetary Dust Particles (Idps)mentioning

confidence: 99%

“…In an initial study, photolysis products from interstellar ice analogs comprised only of small molecules (no PAHs) were studied. Various ice analog mixtures containing H 2 O, CO, NH 3 , CH 3 OH, CH 4 , and C 2 H 2 were exposed to both UV and solar radiation (41). Using L 2 MS, we detected a complex mixture of PAH photoproducts that contained evidence of alkylation, hydrogenation, and in some cases the addition of nitrogen (i.e., -NH 2 , -CN, or -NC).…”

Section: Interplanetary Dust Particles (Idps)mentioning

confidence: 99%

Laser mass spectrometric detection of extraterrestrial aromatic molecules: Mini-review and examination of pulsed heating effects

Spencer

Hammond

Zare

2008

Proc. Natl. Acad. Sci. U.S.A.

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Laser mass spectrometry is a powerful tool for the sensitive, selective, and spatially resolved analysis of organic compounds in extraterrestrial materials. Using microprobe two-step laser mass spectrometry ( L 2 MS), we have explored the organic composition of many different exogenous materials, including meteorites, interplanetary dust particles, and interstellar ice analogs, gaining significant insight into the nature of extraterrestrial materials. Recently, we applied L 2 MS to analyze the effect of heating caused by hypervelocity particle capture in aerogel, which was used on the NASA Stardust Mission to capture comet particles. We show that this material exhibits complex organic molecules upon sudden heating. Similar pulsed heating of carbonaceous materials is shown to produce an artifactual fullerene signal. We review the use of L 2 MS to investigate extraterrestrial materials, and we discuss its recent application to characterize the effect of pulsed heating on samples of interest. (not from Earth), including meteorites, interplanetary dust particles (IDPs), and cometary coma dust, is a fascinating endeavor, and its pursuit can significantly increase our knowledge of planetary formation and interstellar chemistry. Several factors make this task challenging, including sample acquisition in a manner that does not alter compounds and analysis of micrometer-scale samples. Mass spectrometry (MS) offers one means of meeting these criteria. In the past, MS instruments have flown on missions to outer space and the surrounding planets. Notably, the NASA Viking Landers, which touched down on Mars in 1976, used gas chromatography followed by MS to gain the first analysis of the Martian atmosphere (1). MS investigations in space have enabled the understanding that planets exchange material and, in particular, that Earth has received meteorites from the moon and Mars. Much information about our surroundings has been gained by the MS analysis of extraterrestrial materials.Laser MS techniques have particular utility when analyzing low concentrations of organic compounds on complex surfaces and particulates, which are often encountered with extraterrestrial materials. In general, these techniques are able to perform spatially resolved, micrometer-scale surface analyses and have achieved sensitivities in the subattomole regime (2). Most commercial laser MS instrumentation uses one laser pulse, to both thermally desorb surface material and ionize resulting gaseous compounds. A matrix is often added to the sample to facilitate desorption, such as in matrix-assisted laser desorption/ionization (MALDI) (3, 4). Less widespread, because of an increased complexity and specificity, are laser MS techniques that use two lasers, one for sample desorption and one for ionization (2). This two-step laser MS can be used to selectively detect specific organic compound classes with high sensitivity and does not require matrix addition. Only femtograms of surface material are removed during desorption, minimally altering the sample and pe...

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Ultraviolet Photoprocessing of Interstellar Dust Mantles as a Source of Polycyclic Aromatic Hydrocarbons and Other Conjugated Molecules

Cited by 74 publications

References 29 publications

Vacuum ultraviolet photochemistry of solid acetylene: a multispectral approach

Vacuum ultraviolet photochemistry of solid acetylene: a multispectral approach

AKARI view of star formation in NGC 1313

Laser mass spectrometric detection of extraterrestrial aromatic molecules: Mini-review and examination of pulsed heating effects

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