| 1. |
- Dubernet, M. L., et al.
(författare)
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Virtual atomic and molecular data centre
- 2010
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - 0022-4073 .- 1879-1352. ; 111:15, s. 2151-2159
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Tidskriftsartikel (refereegranskat)abstract
- The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) is a European Union funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a secure, documented, flexible and interoperable e-science environment-based interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. It will also provide a forum for training potential users and dissemination of expertise worldwide. This review describes the scope of the VAMDC project; it provides a survey of the atomic and molecular data sets that will be included plus a discussion of how they will be integrated. Some applications of these data are also discussed.
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| 2. |
- Kumar, S. S., et al.
(författare)
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PHOTODETACHMENT AS A DESTRUCTION MECHANISM FOR CN- AND C3N- ANIONS IN CIRCUMSTELLAR ENVELOPES
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 776:1, s. 25-
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Tidskriftsartikel (refereegranskat)abstract
- Absolute photodetachment cross sections of two anions of astrophysical importance CN- and C3N- were measured to be (1.18 +/- (0.03)(stat)(0.17)(sys)) x 10(-17) cm(2) and (1.43 +/- (0.14)(stat)(0.37)(sys)) x 10(-17) cm(2), respectively, at the ultraviolet (UV) wavelength of 266 nm (4.66 eV). These relatively large values of the cross sections imply that photodetachment can play a major role in the destruction mechanisms of these anions particularly in photon-dominated regions. We have therefore carried out model calculations using the newly measured cross sections to investigate the abundance of these molecular anions in the cirumstellar envelope of the carbon-rich star IRC+10216. The model predicts the relative importance of the various mechanisms of formation and destruction of these species in different regions of the envelope. UV photodetachment was found to be the major destruction mechanism for both CN- and C3N- anions in those regions of the envelope, where they occur in peak abundance. It was also found that photodetachment plays a crucial role in the degradation of these anions throughout the circumstellar envelope.
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| 3. |
- Suutarinen, A., et al.
(författare)
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CH abundance gradient in TMC-1
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 531, s. A121-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentaryforms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbonatoms and simple hydrocarbon ions.Methods. We observed the 9-cm Λ-doubling lines of CH along the dense filament of TMC-1. The CH column densities were comparedwith the total H2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH columndensities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physicalconditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretationof the observed OH/CH abundance ratios.Results. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CHabundance relative to H2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10−8, to the southeastwhere it reaches a value of 2.0 × 10−8. The OH and CH column densities are well correlated, and we obtained OH/CH abundanceratios of ∼16–20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to berelated to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar productionand destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances ina low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament.Conclusions. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of alarge CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.
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| 4. |
- Vigren, Erik, et al.
(författare)
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Dissociative Recombination of Protonated Formic Acid : Implications for Molecular Cloud and Cometary Chemistry
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 709:2, s. 1429-1434
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Tidskriftsartikel (refereegranskat)abstract
- At the heavy ion storage ring CRYRING in Stockholm, Sweden, we have investigated the dissociative recombination of DCOOD2+ at low relative kinetic energies, from similar to 1 meV to 1 eV. The thermal rate coefficient has been found to follow the expression k(T) = 8.43 x 10(-7) (T/300)(-0.78) cm(3) s(-1) for electron temperatures, T, ranging from similar to 10 to similar to 1000 K. The branching fractions of the reaction have been studied at similar to 2 meV relative kinetic energy. It has been found that similar to 87% of the reactions involve breaking a bond between heavy atoms. In only 13% of the reactions do the heavy atoms remain in the same product fragment. This puts limits on the gas-phase production of formic acid, observed in both molecular clouds and cometary comae. Using the experimental results in chemical models of the dark cloud, TMC-1, and using the latest release of the UMIST Database for Astrochemistry improves the agreement with observations for the abundance of formic acid. Our results also strengthen the assumption that formic acid is a component of cometary ices.
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| 5. |
- Wirström, Eva, 1977, et al.
(författare)
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Observational tests of interstellar methanol formation
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 533, s. A24-
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Tidskriftsartikel (refereegranskat)abstract
- Context. It has been established that the classical gas-phase production of interstellar methanol (CH(3)OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces. Aims. While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs). Methods. We have observed the rotational transition quartets J = 2(K) - 1(K) of (12)CH(3)OH and (13)CH(3)OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1-0 transitions of (12)C(18)O and (13)C(18)O were observed towards some of these sources. We use the (12)C/(13)C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH(3)OH and CO. If not, the ratio should be higher in CH(3)OH due to (13)C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol. Results. We show that the (12)C/(13)C isotopic ratio is very similar in gas-phase CH(3)OH and C(18)O, on the spatial scale of about 40 '', towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity. Conclusions. While the (12)C/(13)C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive.
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