PAHs and the Universe最新文献

{"title":"Laboratory Spectroscopy of Protonated PAH Molecules Relevant For Interstellar Chemistry","authors":"O. Dopfer","doi":"10.1051/EAS/1146010","DOIUrl":"https://doi.org/10.1051/EAS/1146010","url":null,"abstract":"In this contribution, we summarize the recent progress made in recording laboratory infrared (IR) spectra of protonated polycyclic aromatic hydrocarbon molecules (H + PAH) in the gas phase. The IR spectra of a large variety of H + PAH species ranging from benzene to coronene have been obtained by various variants of photodissociation spectroscopy. The employed techniques include single-photon IR photodissociation (IRPD) of tagged H + PAH ions and IR multiple-photon dissociation (IRMPD) of bare H + PAH ions. The comparison of the laboratory IR spectra with astronomical spectra supports the hypothesis that H + PAH ions are possible carriers of the unidentified IR emission (UIR) bands. Moreover, the spectra provide detailed information about the geometric and electronic structure as well as the chemical reactivity and stability of these fundamental hydrocarbon ions.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129018866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PAH Evolution in the Harsh Environment of the ISM","authors":"H. Kaneda, T. Onaka, I. Sakon, D. Ishihara, A. Mouri, M. Yamagishi, A. Yasuda","doi":"10.1051/EAS/1146017","DOIUrl":"https://doi.org/10.1051/EAS/1146017","url":null,"abstract":"We review observational results of PAH emission in harsh interstellar environments, which are mostly based on recent works by Spitzer and AKARI. The harsh environments include shock regions in our Galaxy, the ionized superwinds and haloes of external galaxies, and the hot plasmas of elliptical galaxies. Owing to the unprecedented high sensitivity for PAH emission with Spitzer and AKARI, it is found that an appreciable amount of PAHs are present in some cases with such hostile conditions. Some of them exhibit unusual PAH interband strength ratios, reflecting either evolution of PAHs or physical conditions of the ISM. The distribution of the PAH emission, as compared to that of dust emission, is shown to discuss their ways of evolution and survival.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129167080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PAHs and the Chemistry of the ISM","authors":"V. Bierbaum, V. L. Page, T. Snow","doi":"10.1051/EAS/1146044","DOIUrl":"https://doi.org/10.1051/EAS/1146044","url":null,"abstract":"This review describes five categories of the reactions of polycyclic aromatic hydrocarbons, including photochemistry, electron attachment/detachment, recombination processes, radical reactions, and ion-neutral chemistry. For each class of reaction, an overview of the studies and their general results are presented, as well as references to the literature. The thermochemistry of PAHs and relevant species is described, including bond dissociation energies, ionization energies, electron affinities, basicities, acidities, and the interrelationships of these quantities. Modeling of the chemistry of PAHs and their ions is discussed for both diffuse and dark clouds. The role of PAH cations in the catalytic formation of molecular hydrogen is considered. Finally, this review concludes with a discussion of current challenges in the chemical characterization of PAHs, and a perspective for future studies.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124341790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Spitzer Surveys of the Small Magellanic Cloud: Insights into the Life-Cycle of Polycyclic Aromatic Hydrocarbons","authors":"K. Sandstrom, A. Bolatto, B. Draine, C. Bot, S. Stanimirović","doi":"10.1051/EAS/1146023","DOIUrl":"https://doi.org/10.1051/EAS/1146023","url":null,"abstract":"We present the results of modeling dust spectral energy distributions (SEDs) across the Small Magellanic Cloud (SMC) with the aim of mapping the distribution of polycyclic aromatic hydrocarbons (PAHs) in a low-metallicity environment. Using Spitzer Survey of the SMC (S 3 MC) photometry from 3.6 to 160 µm over the main star-forming regions of the Wing and Bar of the SMC along with spectral mapping observations from 5 to 38 µm from the Spitzer Spectroscopic Survey of the Small Magellanic Cloud (S 4 MC) in selected regions, we model the dust spectral energy distribution and emission spectrum to determine the fraction of dust in PAHs across the SMC. We use the regions of overlaping photometry and spectroscopy to test the reliability of the PAH fraction as determined from SED fits alone. The PAH fraction in the SMC is low compared to the Milky Way and variable– with relatively high fractions (qPAH� 1 − 2%) in molecular clouds and low fractions in the diffuse ISM (average hqPAHi = 0.6%). We use the map of PAH fraction across the SMC to test a number of ideas regarding the production, destruction and processing of PAHs in the ISM. We find weak or no correlation between the PAH fraction and the distribution of carbon AGB stars, the location of supergiant H I shells and young supernova remnants, and the turbulent Mach number. We find that the PAH fraction is correlated with CO intensity, peaks in the dust surface density and the molecular gas surface density as determined from 160 µm emission. The PAH fraction is high in regions of active star-formation, as predicted by its correlation with molecular gas, but is supressed in H II regions. Because the PAH fraction in the diffuse ISM is generally very low–in accordance with previous work on modeling the integrated SED of the SMC–and the PAH fraction is relatively high in molecular regions, we suggest that PAHs are destroyed in the diffuse ISM of the SMC and/or PAHs are forming in molecular clouds. We discuss the implications of these observations for our understanding of the PAH life cycle, particularly in low-metallicity and/or primordial galaxies. Subject headings: dust, extinction — infrared: ISM — Magellanic Clouds","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116175558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Summary of the Meeting","authors":"A. Omont","doi":"10.1051/EAS/1146048","DOIUrl":"https://doi.org/10.1051/EAS/1146048","url":null,"abstract":"This symposium has shown that the field of astrophysical PAHs remains extremely active and lively. Thanks to Spitzer Space Telescope, the number of PAH papers has spectacularly increased, including now up to the young Universe. Laboratory and theoretical works have progressed in proportion. Salient features of the six sessions of the symposium are briefly reviewed. Comprehensive analyses of the rich and complex infrared spectra of interstellar PAHs are now well established, based on a large database of observational data. PAHs are fully confirmed as excellent tracers of star formation, but their emission strongly depends on metallicity. Various observations, especially in harsh environments, have confirmed the complexity of the lifecycle of PAHs in space, and the need for multiple formation modes. Electronic properties remain a major issue for astronomical PAHs, including their possible connection with the diffuse interstellar bands, and the possible importance of protonated PAHs. Progress in studying complex carbonaceous compounds, such as those of various soots, and in synthesizing very large PAHs may give important clues for understanding interstellar PAHs. Significant progress was also reported in modeling the important role of PAHs in the physics and chemistry of the interstellar medium.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"37 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121694489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analyzing Astronomical Observations with the NASA Ames PAH Database","authors":"J. Cami, C. Boersma, E. Peeters, C. Bauschlicher, D. Hudgins, L. Allamandola","doi":"10.1051/EAS/1146012","DOIUrl":"https://doi.org/10.1051/EAS/1146012","url":null,"abstract":"We use the NASA Ames Polycyclic Aromatic Hydrocarbon (PAH) infrared spectroscopic database to model infared emission of PAHs following absorption of a UV photon. We calculate emission spectra resulting from the full cooling cascade for each species in the database. Using a least squares approach, we can find out what PAH mixtures best reproduce a few typical astronomical observations representing the different classes of UIR spectra. We find that we can reproduce the observed UIR spectra in the wavelength range 6–14 μ m, offering support for the hypothesis that the UIR bands are indeed due to vibrational modes of PAHs and related molecular species. Spectral decompositions of our best fit models confirm and reinforce several earlier results: (i) the 6.2 μ m band requires a significant contribution of nitrogen-substituted PAHs (PANHs); (ii) the reported components and their variations in the 7.7 μ m band are indicative of changes in the size distribution of the contributing molecules; (iii) there is a significant contribution of anions to the 7.7 μ m band; (iv) the 11.2 μ m band is due to large, neutral and pure PAHs; (v) the 11.0 μ m band is due to large PAH cations.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114385441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computational IR Spectroscopy for PAHs: From the Early Years to the Present Status","authors":"F. Pauzat","doi":"10.1051/EAS/1146008","DOIUrl":"https://doi.org/10.1051/EAS/1146008","url":null,"abstract":"In the long story of interstellar PAHs, computations have played and are still playing a fundamental role in connection with ex- periments and observations. From the very first calculations of the IR spectra of small PAHs in the late eighties to the more recent ones, ev- ery aspect of the research linked to the PAH hypothesis has evolved dramatically: the size and the variety of the molecules considered, the techniques used, the precision of the astronomical observations ...The initial landscape has completely changed though the quest is still the same, that is to correlate the so-called UIR bands spectra ubiquitous in the ISM (Inter Stellar Medium) with a chemical family of molecules, the PAHs. An historical review of the 25 years of this quest is presented here, focusing on the computational part.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126551260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interaction of Atomic Hydrogen with Carbon Grains","authors":"V. Mennella","doi":"10.1051/EAS/1146040","DOIUrl":"https://doi.org/10.1051/EAS/1146040","url":null,"abstract":"Laboratory studies on the interaction of atomic hydrogen with aliphatic and aromatic\u0000 hydrogenated carbon grains are discussed. When exposed to atomic hydrogen, both types of\u0000 hydrogenated carbon grains act as catalysts for molecular hydrogen formation. In the first\u0000 case, an exchange reaction with hydrogen chemisorbed in aliphatic carbon sites is the\u0000 formation route to H 2 formation. For aromatic carbon grains, the formation of\u0000 molecular hydrogen takes place through a two-step reaction sequence: 1) super\u0000 hydrogenation of the aromatic carbon islands of grains 2) exchange reactions on these\u0000 islands. This mechanism represents a good approximation of molecular hydrogen formation on\u0000 large neutral PAHs.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"50 3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134043208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From PAHs to Solid Carbon","authors":"C. Jäger, H. Mutschke, T. Henning, F. Huisken","doi":"10.1051/EAS/1146031","DOIUrl":"https://doi.org/10.1051/EAS/1146031","url":null,"abstract":"Carbonaceous grains represent a major component of cosmic dust. The review will summarize new results in laboratory investiga- tions of carbonaceous dust components. The nanometer-sized carbon particles are supposed to represent a blend of differently structured carbon including graphitic, diamond-like, fullerene-like and chain-like components on a subnanometer or nanometer scale. Recent models used to explain the structure of gas-phase condensed carbon nano- particles are discussed. Possible formation pathways of carbonaceous grains from molecular components and clusters and the role of poly- cyclic aromatic hydrocarbons (PAHs) and fullerenes are disclosed.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127081841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PAH and Dust Processing in Supernova Remnants","authors":"J. Rho, M. Andersen, A. Tappe, W. Reach, J. Bernard, J. Hewitt","doi":"10.1051/EAS/1146018","DOIUrl":"https://doi.org/10.1051/EAS/1146018","url":null,"abstract":"I present observations of shock-processed PAHs and dust in supernova remnants (SNRs).\u0000 Supernova shocks are one of the primary sites destroying, fragmenting and altering\u0000 interstellar PAHs and dust. Studies of PAHs through supernova shocks had been limited\u0000 because of confusion with PAHs in background emission. Spitzer\u0000 observations with high sensitivity and resolution allow us to separate PAHs\u0000 associated with the SNRs and unrelated, Galactic PAHs. In the young SNR N132D, PAH\u0000 features are detected with a higher PAH ratio of 15–20/7.7 μ m than those\u0000 of other astronomical objects, and we suggest large PAHs have survived behind the shock.\u0000 We present the spectra of additional 14 SNRs observed with Spitzer IRS\u0000 and MIPS SED covering the range of 5–90 μ m. Bright PAH features from 6.2\u0000 to 15–20 μ m are detected from many of SNRs which emit molecular hydrogen\u0000 lines, indicating that both large and small PAHs survive in low velocity shocks. We\u0000 observe a strong correlation between PAH detection and carbonaceous small grains, while a\u0000 few SNRs with dominant silicate dust lack PAH features. We characterize PAHs depending on\u0000 the shock velocity, preshock density and temperature of hot gas, and discuss PAH and dust\u0000 processing in shocks and implication of PAH and dust cycles in ISM.","PeriodicalId":197011,"journal":{"name":"PAHs and the Universe","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126649821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}