Molecular Astrophysics最新文献

{"title":"The formation of astrophysical Mg-rich silicate dust","authors":"Christopher M. Mauney,&nbsp;Davide Lazzati","doi":"10.1016/j.molap.2018.03.002","DOIUrl":"10.1016/j.molap.2018.03.002","url":null,"abstract":"<div><p>We present new results for ground-state candidate energies of Mg-rich olivine (MRO) clusters and use the binding energies of these clusters to determine their nucleation rates in stellar outflows, with particular interest in the environments of core-collapse supernovae (CCSNe). Low-lying structures of clusters (Mg₂SiO₄)_<em>n</em> 2 ≤ <em>n</em> ≤ 13 are determined from a modified minima hopping algorithm using an empirical silicate potential in the Buckingham form. These configurations are further refined and optimized using the density functional theory code Quantum Espresso. Utilizing atomistic nucleation theory, we determine the critical size and nucleation rates of these clusters. We find that configurations and binding energies in this regime are very dissimilar from those of the bulk lattice. Clusters grow with SiO₄–MgO layering and exhibit only global, rather than local, symmetries. When compared to classical nucleation theory we find suppressed nucleation rates at most temperatures and pressures, with enhanced nucleation rates at very large pressures. This implies a slower progression of silicate dust formation in stellar environments than previously assumed.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"12 ","pages":"Pages 1-9"},"PeriodicalIF":0.0,"publicationDate":"2018-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2018.03.002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85967288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transmission spectroscopy with the ACE-FTS infrared spectral atlas of Earth: A model validation and feasibility study","authors":"Franz Schreier ,&nbsp;Steffen Städt ,&nbsp;Pascal Hedelt ,&nbsp;Mareike Godolt","doi":"10.1016/j.molap.2018.02.001","DOIUrl":"10.1016/j.molap.2018.02.001","url":null,"abstract":"<div><p>Infrared solar occultation measurements are well established for remote sensing of Earth’s atmosphere, and the corresponding primary transit spectroscopy has turned out to be valuable for characterization of extrasolar planets. Our objective is an assessment of the detectability of molecular signatures in Earth’s transit spectra.</p><p><span>To this end, we take a limb sequence of representative cloud-free transmission spectra recorded by the space-borne ACE-FTS Earth observation mission (Hughes et al., ACE<span> infrared spectral atlases of the Earth’s atmosphere, JQSRT 2014) and combine these spectra to the effective height of the atmosphere. These data are compared to spectra modeled with an atmospheric radiative transfer line-by-line infrared code to study the impact of individual molecules, </span></span>spectral resolution, the choice of auxiliary data, and numerical approximations. Moreover, the study serves as a validation of our infrared radiative transfer code.</p><p><span><span>The largest impact is due to water, carbon dioxide, ozone, methane, nitrous oxide, nitrogen, </span>nitric acid, oxygen, and some chlorofluorocarbons (CFC11 and CFC12). The effect of further molecules considered in the modeling is either marginal or absent. The best matching model has a mean residuum of 0.4 km and a maximum difference of 2 km to the measured effective height. For a quantitative estimate of visibility and detectability we consider the maximum change of the residual spectrum, the relative change of the residual norm, the additional transit depth, and signal-to-noise ratios for a </span>JWST setup. In conclusion, our study provides a list of molecules that are relevant for modeling transmission spectra of Earth-like exoplanets and discusses the feasibility of retrieval.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"11 ","pages":"Pages 1-22"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2018.02.001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74751146","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":"Fine-structure resolved rotational transitions and database for CN+H2 collisions","authors":"Hannah Burton ,&nbsp;Ryan Mysliwiec ,&nbsp;Robert C. Forrey ,&nbsp;B.H. Yang ,&nbsp;P.C. Stancil ,&nbsp;N. Balakrishnan","doi":"10.1016/j.molap.2018.03.001","DOIUrl":"10.1016/j.molap.2018.03.001","url":null,"abstract":"<div><p>Cross sections and rate coefficients for CN+H₂<span> collisions are calculated using the coupled states (CS) approximation. The calculations are benchmarked against more accurate close-coupling (CC) calculations for transitions between low-lying rotational states. Comparisons are made between the two formulations for collision energies greater than 10 cm</span>⁻¹<span>. The CS approximation is used to construct a database which includes highly excited rotational states that are beyond the practical limitations of the CC method. The database includes fine-structure resolved rotational quenching transitions for </span><span><math><mrow><mi>v</mi><mo>=</mo><mn>0</mn></mrow></math></span> and <em>j</em> ≤ 40, where <em>v</em> and <em>j</em><span> are the vibrational and rotational quantum numbers of the initial state of the CN molecule. Rate coefficients are computed for both para-H</span>₂ and ortho-H₂ colliders. The results are shown to be in good agreement with previous calculations, however, the rates are substantially different from mass-scaled CN+He rates that are often used in astrophysical models.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"11 ","pages":"Pages 23-32"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2018.03.001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90739142","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":"Providing theoretical data for detection of four formamidic acid isomers in astrophysical media","authors":"R.M. Vichietti,&nbsp;A.B.F. da Silva,&nbsp;R.L.A. Haiduke","doi":"10.1016/j.molap.2018.01.001","DOIUrl":"10.1016/j.molap.2018.01.001","url":null,"abstract":"<div><p><span>We present a theoretical study, so that molecular data (geometrical parameters, vibrational frequencies<span>, infrared intensities, electronic energies, enthalpies, and Gibbs energies) of four formamidic acid (FA) isomers (labeled here as FA1, FA2, FA3, and FA4) and formamide (HCONH</span></span>₂<span><span>) are obtained from CCSD/cc-pVTZ, CCSD/aug-cc-pVTZ, CCSD/cc-pVQZ, and CCSD(T)/cc-pVTZ calculations. Furthermore, on the basis of insufficient or even lacking theoretical and experimental results in the literature, we employed the aforementioned theory levels to determine benchmark values of dipole moments<span> and rotational constants for these four FA isomers in order to contribute for their detection in astrophysical environments. Besides, we provide for the first time data about forward and reverse rate constants (200–4000 K) and Arrhenius’ parameters for each interconversion reaction between pairs of FA isomers as well as for the tautomeric process involving FA4 and formamide, which were calculated from a Complete Basis Set (CBS) extrapolation equation obtained at CCSD/cc-pVTZ optimized geometries. Our </span></span>kinetic analysis indicated a faster interconversion between the FA structures in comparison with the FA4 ↔ HCONH</span>₂ process, suggesting that these isomers could co-exist in astrophysical media. Finally, we estimated that these isomers may be detected with relative abundances, [FA<em>_x</em>]/[HCONH₂] (<em>x</em> = 1, 2, 3, and 4), between ∼0.01 and ∼0.1% in astrophysical sources at chemical equilibrium conditions and temperatures around 1000 K. However, these ratios can become as high as ∼1, ∼3, and ∼5%, respectively, in hotter regions with temperatures around 2000, 3000, and 4000 K (expected, for example, in massive star-forming regions).</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"10 ","pages":"Pages 1-10"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2018.01.001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79918737","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":"First-principles study of the formation of glycine-producing radicals from common interstellar species","authors":"Akimasa Sato ,&nbsp;Yuya Kitazawa ,&nbsp;Toshiro Ochi ,&nbsp;Mitsuo Shoji ,&nbsp;Yu Komatsu ,&nbsp;Megumi Kayanuma ,&nbsp;Yuri Aikawa ,&nbsp;Masayuki Umemura ,&nbsp;Yasuteru Shigeta","doi":"10.1016/j.molap.2018.01.002","DOIUrl":"10.1016/j.molap.2018.01.002","url":null,"abstract":"<div><p><span>Glycine, the simplest amino acid<span>, has been intensively searched for in molecular clouds<span>, and the comprehensive clarification of the formation path of interstellar glycine is now imperative. Among all the possible glycine formation pathways, we focused on the radical pathways revealed by Garrod (2013). In the present study, we have precisely investigated all the chemical reaction steps related to the glycine formation processes based on state-of-the-art density functional theory (DFT) calculations. We found that two reaction pathways require small activation barriers (Δ</span></span></span><em>E^‡</em> ≤ 7.75 kJ mol^–1<span><span><span>), which demonstrates the possibility of glycine formation even at low temperatures in interstellar space if the radical species are generated. The origin of carbon and nitrogen in the glycine backbone and their combination patterns are further discussed in relation to the formation mechanisms. According to the clarification of the atomic correspondence between glycine and its potential parental molecules, it is shown that the nitrogen and two carbons in the glycine can originate in three common </span>interstellar molecules, methanol, </span>hydrogen cyanide, and ammonia, and that the source molecules of glycine can be described by any of their combinations. The glycine formation processes can be categorized into six patterns. Finally, we discussed two other glycine formation pathways expected from the present DFT calculation results.</span></p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"10 ","pages":"Pages 11-19"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2018.01.002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75999084","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":"H2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations","authors":"Valentine Wakelam ,&nbsp;Emeric Bron ,&nbsp;Stephanie Cazaux ,&nbsp;Francois Dulieu ,&nbsp;Cécile Gry ,&nbsp;Pierre Guillard ,&nbsp;Emilie Habart ,&nbsp;Liv Hornekær ,&nbsp;Sabine Morisset ,&nbsp;Gunnar Nyman ,&nbsp;Valerio Pirronello ,&nbsp;Stephen D. Price ,&nbsp;Valeska Valdivia ,&nbsp;Gianfranco Vidali ,&nbsp;Naoki Watanabe","doi":"10.1016/j.molap.2017.11.001","DOIUrl":"10.1016/j.molap.2017.11.001","url":null,"abstract":"<div><p>Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H₂ formation in a variety of interstellar environments.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"9 ","pages":"Pages 1-36"},"PeriodicalIF":0.0,"publicationDate":"2017-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2017.11.001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78012040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Laboratory spectra of hot molecules: Data needs for hot super-Earth exoplanets","authors":"Jonathan Tennyson,&nbsp;Sergei N. Yurchenko","doi":"10.1016/j.molap.2017.05.002","DOIUrl":"10.1016/j.molap.2017.05.002","url":null,"abstract":"<div><p>The majority of stars are now thought to support exoplanets. Many of those exoplanets discovered thus far are categorized as rocky objects with an atmosphere. Most of these objects are however hot due to their short orbital period. Models suggest that water is the dominant species in their atmospheres. The hot temperatures are expected to turn these atmospheres into a (high pressure) steam bath containing remains of melted rock. The spectroscopy of these hot rocky objects will be very different from that of cooler objects or hot gas giants. Molecules suggested to be important for the spectroscopy of these objects are reviewed together with the current status of the corresponding spectroscopic data. Perspectives of building a comprehensive database of linelist/cross sections applicable for atmospheric models of rocky super-Earths as part of the ExoMol project are discussed. The quantum-mechanical approaches used in linelist productions and their challenges are summarized.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"8 ","pages":"Pages 1-18"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2017.05.002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77225412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kekulene: Structure, stability and nature of H•••H interactions in large PAHs","authors":"J. Poater ,&nbsp;J. Paauwe ,&nbsp;S. Pan ,&nbsp;G. Merino ,&nbsp;C. Fonseca Guerra ,&nbsp;F.M. Bickelhaupt","doi":"10.1016/j.molap.2017.05.003","DOIUrl":"10.1016/j.molap.2017.05.003","url":null,"abstract":"<div><p><span><span><span>We have quantum chemically analyzed how the stability of small and larger polycyclic aromatic hydrocarbons<span> (PAHs) is determined by characteristic patterns in their structure using density functional theory at the BLYP/TZ2P level. In particular, we focus on the effect of the nonbonded H•••H interactions that occur in the bay region of kinked (or armchair) PAHs, but not in straight (or zigzag) PAHs. Model systems comprise </span></span>anthracene, </span>phenanthrene, and kekulene as well as derivatives thereof. Our main goals are: (1) to explore how nonbonded H•••H interactions in armchair configurations of kinked PAHs affect the geometry and stability of PAHs and how their effect changes as the number of such interactions in a PAH increases; (2) to understand the extent of stabilization upon the substitution of a bay C</span><img>H fragment by either C^• or N; and (3) to examine the origin of such stabilizing/destabilizing interactions.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"8 ","pages":"Pages 19-26"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2017.05.003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79828683","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":"On the spectroscopic constants, first electronic state, vibrational frequencies, and isomerization of hydroxymethylene (HCOH+)","authors":"Riley A. Theis,&nbsp;Ryan C. Fortenberry","doi":"10.1016/j.molap.2017.06.001","DOIUrl":"10.1016/j.molap.2017.06.001","url":null,"abstract":"<div><p>The hydroxymethylene cation (HCOH<span><math><msup><mrow></mrow><mo>+</mo></msup></math></span><span>) is believed to be chemically independent of the more stable formaldehyde cation isomer in interstellar chemistry and may likely be a precursor to methanol in chemical reaction networks. Previous work is corroborated here showing that the </span><em>trans</em><span> conformer of HCOH</span><span><math><msup><mrow></mrow><mo>+</mo></msup></math></span> is 3.48 kcal/mol lower than the <em>cis</em><span> on the potential energy surface<span>. The small energy difference between the conformers and the much larger dipole moment of </span></span><em>cis</em>-HCOH<span><math><msup><mrow></mrow><mo>+</mo></msup></math></span> (2.73 D) make this conformer more likely to be observed than <em>trans</em>-HCOH<span><math><msup><mrow></mrow><mo>+</mo></msup></math></span><span> via telescopic rotational spectroscopy<span>. A strong adiabatic shift is also predicted in the first electronic excitation into the 1 </span></span>²<em>A</em>′′/2 ²<em>A</em> state out of either conformer into a <em>C</em>₁<span> structure reducing the excitation wavelength from the near-ultraviolet all the way into the near-infrared. The full set of fundamental vibrational frequencies are also computed here at high-level. The 3306.0 cm</span><span><math><msup><mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math></span> and 3225.3 cm<span><math><msup><mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math></span> hydroxide stretches, respective of bare <em>trans</em>- and <em>cis</em>-HCOH<span><math><mrow><msup><mrow></mrow><mo>+</mo></msup><mo>,</mo></mrow></math></span> are in agreement with previous theory but are significantly higher than the frequencies determined from previous experiment utilizing argon tagging techniques. This shift is likely because the proton-bound complex created with the argon tag reduces the experimental frequencies. Lower-level computations including the argon tag bring the hydroxide stretches much closer to the experimental frequencies indicating that the predicted frequencies for bare HCOH<span><math><msup><mrow></mrow><mo>+</mo></msup></math></span> are likely well-described.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"8 ","pages":"Pages 27-35"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2017.06.001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82799886","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":"Helium broadened propane absorption cross sections in the far-IR","authors":"A. Wong ,&nbsp;B. Billinghurst ,&nbsp;P.F. Bernath","doi":"10.1016/j.molap.2017.06.003","DOIUrl":"10.1016/j.molap.2017.06.003","url":null,"abstract":"<div><p>Infrared absorption spectra for pure and He broadened propane have been recorded in the far-IR region (650-1300<!--> <!-->cm⁻¹) at the Canadian Light Source (CLS) facility using either the synchrotron or internal glowbar source depending on the required resolution. The measurements were made for 4 temperatures in the range 202–292<!--> <!-->K and for 3 pressures of He broadening gas up to 100<!--> <!-->Torr. Infrared absorption cross sections are derived from the spectra and the integrated cross sections are within 10<!--> <!-->% of the corresponding values from the Pacific Northwest National Laboratory (PNNL) for all temperatures and pressures.</p></div>","PeriodicalId":44164,"journal":{"name":"Molecular Astrophysics","volume":"8 ","pages":"Pages 36-39"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.molap.2017.06.003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73891127","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}