共查询到20条相似文献,搜索用时 15 毫秒
1.
A fairly complete but limited set of gas phase reactions involving nitrogen-bearing molecules is linked to a simple model of grain surface reactions. Calculations are performed attempting to simulate the nitrogen chemistry in interstellar clouds of low and high density. While it appears probable that grain surface reactions contribute to the chemistry in both régimes, conclusive evidence awaits observational and theoretical developments. 相似文献
2.
S. B. Charnley 《Astrophysics and Space Science》1995,224(1-2):441-442
A study has been undertaken of the gas-grain chemistry of protostellar disks which are sufficiently cool that in the outer regions, where the gas density is less than 1013 cm–3 and the ionization rate highest, a bimolecular chemistry resembling that of dark clouds can occur. Since the gas-grain collision rate is so high, outgassing mantle molecules effectively determine the gas phase composition at any position in the disk. In contrast to previous work, a detailed gas phase chemistry is considered along with the accretion and desorption of mantle species which is controlled locally by the dust temperature. 相似文献
3.
The contribution of exothermic ion and neutral chemistry to Titan's corona is studied. The production rates for fast neutrals N2, CH4, H, H2, 3CH2, CH3, C2H4, C2H5, C2H6, N(4S), NH, and HCN are determined using a coupled ion and neutral model of Titan's upper atmosphere. After production, the formation of the suprathermal particles is modeled using a two-stream simulation, as they travel simultaneously through a thermal mixture of N2, CH4, and H2. The resulting suprathermal fluxes, hot density profiles, and energy distributions are compared to the N2 and CH4 INMS exospheric data presented in [De La Haye, V., Waite Jr., J.H., Johnson, R.E., Yelle, R.V., Cravens, T.E., Luhmann, J.G., Kasprzak, W.T., Gell, D.A., Magee, B., Leblanc, F., Michael, M., Jurac, S., Robertson, I.P., 2007. J. Geophys. Res., doi:10.1029/2006JA012222, in press], and are found insufficient for producing the suprathermal populations measured. Global losses of nitrogen atoms and carbon atoms in all forms due to exothermic chemistry are estimated to be and . 相似文献
4.
The contribution from different types of nanocluster is examined as being responsible for the inhomogeneous broadening in the normalized interstellar extinction curve. These are (i) molecules of aromatic hydrocarbons, (ii) particles of amorphous (diamond-like) carbon, (iii) particles of glassy carbon, (iv) particles of amorphous carbon encapsulated in glassy carbon and (v) particles of amorphous carbon containing graphitized inclusions. It is shown that particles of encapsulated amorphous carbon together with particles of glassy carbon may contribute to the absorption band at 217.5 nm (5.67 eV) for a ratio between the size of the amorphous carbon core to its overall exterior in the range 0.6–0.8. Particles of amorphous diamond-like carbon containing graphitized inclusions may contribute both to the 217.5-nm absorption band and to the absorption band located at ∼400 nm (3.09 eV). 相似文献
5.
Saito S Yamamoto S Irvine WM Ziurys LM Suzuki H Ohishi M Kaifu N 《The Astrophysical journal》1988,334(2):L113-L116
An asymmetric-top free radical CH2CN, which as a 2B1 ground state, was detected for the first time by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11-10 to 14-13 a-type rotational transitions in the frequency region of 220-260 GHz, and many hyperfine resolved components for the N = 4-3 and 5-4 transitions in the 80 and 100 GHz regions, respectively. The molecular constants, including the rotational constants, centrifugal distortion constants, and spin-rotation coupling constants with centrifugal distortion correction terms were determined from the fine-structure resolved transitions, and the hyperfine coupling constants due to the hydrogen and nitrogen nuclei were obtained from the low-N transitions. As a result we assigned U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1, to the N = 5-4, 4-3, 2-1, and 1-0 transitions with K-1 = 0 of the CH2CN radical. 相似文献
6.
杜福君 《天文和天体物理学研究(英文版)》2021,(3):261-271
Astrochemical modeling is needed for understanding the formation and evolution of interstellar molecules,and for extracting physical information from spectroscopic observations of interstellar clouds.The modeling usually involves the handling of a chemical reaction network and solution of a set of coupled nonlinear ordinary differential equations,which is traditionally done using code written in compiled languages such as Fortran or C/C++.While being computationally efficient,there is room for improvement in the ease of use and interactivity for such an approach.In this work we present a new public code named CHEMPL,which emphasizes interactivity in a modern Python environment,while remaining computationally efficient.Common reaction mechanisms and a three-phase formulation of gasgrain chemistry are implemented by default.It is straightforward to run 0 D models with CHEMPL,and only a small amount of additional code is needed to construct 1 D or higher-dimensional chemical models.We demonstrate its usage with a few astrochemically relevant examples. 相似文献
7.
T. A. Bell S. Viti D. A. Williams I. A. Crawford R. J. Price 《Monthly notices of the Royal Astronomical Society》2005,357(3):961-966
Transient microstructure in the diffuse interstellar medium (ISM) has been observed towards Galactic and extragalactic sources for decades, usually in lines of atoms and ions, and, more recently, in molecular lines. Evidently, there is a molecular component to the transient microstructure. In this paper, we explore the chemistry that may arise in such microstructure. We use a photodissociation region (PDR) code to model the conditions of relatively high density, low temperature, very low visual extinction and very short elapsed time that are appropriate for these objects. We find that there is a well-defined region of parameter space where detectable abundances of molecular species might be found. The best matching models are those where the interstellar microstructure is young (<100 yr), small (∼100 au) and dense (>104 cm−3 ) . 相似文献
8.
Calculations have been performed to determine the abundance ratio of the metastable isomer CH3NC to the stable isomer CH3CN in dense interstellar clouds. According to gas phase, ion-molecule treatments, these molecules are both synthesized via protonated ion precursors. We have calculated the ratio of the formation rates of the protonated precursor ions-- CH3NCH+ and CH3CNH+ --synthesized via the radiative association reaction between CH3+ and HCN, which is thought to the dominant formation process of the two isomeric ions. Our calculations, which involve both ab initio quantum chemistry and equilibrium determinations, lead to a predicted CH3NCH+/CH3CNH+ formation rate ratio between 0.1 and 0.4. If this ratio is maintained in the neutral species formed from the precursor ions, theory predicts a sizable abundance for methyl isocyanide (CH3NC) and lends credence to its tentative observation. 相似文献
9.
Recent cryochemical and photochemical findings for cyanoacetylene and cyanopolyacetylene-related molecules (including various
isomeric species), backed up with quantum-chemical predictions, are analysed. A new class of interstellar molecules, distinguished
by bare (hydrogen-less), unsaturated carbon-nitrogen chains of the general formula C
n
N2 is postulated. It is recommended to look for some relevant IR spectral features in space.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Irvine WM Friberg P Hjalmarson A Ishikawa S Kaifu N Kawaguchi K Madden SC Matthews HE Ohishi M Saito S Suzuki H Thaddeus P Turner BE Yamamoto S Ziurys LM 《The Astrophysical journal》1988,334(2):L107-L111
We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H. 相似文献
11.
12.
Ralf Srama Thomas Stephan Eberhard Grün Norbert Pailer Anton Kearsley Amara Graps Rene Laufer Pascale Ehrenfreund Nicolas Altobelli Kathrin Altwegg Siegfried Auer Jack Baggaley Mark J. Burchell James Carpenter Luigi Colangeli Francesca Esposito Simon F. Green Hartmut Henkel Mihaly Horanyi Annette Jäckel Sascha Kempf Neil McBride Georg Moragas-Klostermeyer Harald Krüger Pasquale Palumbo Andre Srowig Mario Trieloff Peter Tsou Zoltan Sternovsky Oliver Zeile Hans-Peter Röser 《Experimental Astronomy》2009,23(1):303-328
The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We
propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth.
SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board
allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important
constraints for subsequent laboratory analysis.
The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and
inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and
October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection
period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area
of 1 m2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule.
SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar
samples by latest laboratory technologies. 相似文献
13.
M. A. Leitch-Devlin T. J. Millar J. Pickles D. A. Williams 《Astrophysics and Space Science》1976,44(2):385-388
Some recent arguments concerning the relevance of grain surface reactions to interstellar molecule formation are shown to be without foundation. It is probable that surface reactions, gas phase ion-molecule and neutral reactions all contribute to interstellar molecular densities. 相似文献
14.
The production of CH+ in dense interstellar clouds under intense UV irradiation is discussed. A model applicable to the cloud towards the star 20 Tau is described. 相似文献
15.
In recent years, the need to replace rate equations for studying grain-surface chemistry in the modelling of interstellar
clouds has become apparent. In this article, we discuss the three new replacement methods that have been suggested to date,
and contrast their relative strengths and weaknesses.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
17.
Christopher F. McKee 《Astrophysics and Space Science》1986,118(1-2):383-393
Stars inject energy into the interstellar medium (ISM) by radiation, stellar winds, and supernova explosions. This energy injection causes the ISM to be inhomogeneous, which in turn alters the manner in which the energy is transferred through the ISM. A significant fraction of the energy is injected by massive stars, which formHii regions in the ISM. The structure and evolution ofHii regions in a cloudy medium deffers significantly from that in a homogeneous one. The strong stellar winds produced by massive stars form bubbles in the ISM, and the structure of these bubbles is often dominated by the structure of theHii region in which they are embedded. Finally, when the star explodes as a supernova, the evolution and appearance of the resulting remnant is determined by the structure of the bubble andHii region formed by the star during its lifetime.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
18.
《New Astronomy Reviews》2000,44(4-6):375-377
A possibility of obtaining information on small-scale inhomogeneities of the electron component of the local interstellar medium (LISM) was investigated using interstellar scintillations of extragalactic radio sources. We analysed Culgoora array observational variability data of 190 extragalactic radio sources, covering most of the sky, at 80 and 160 MHz. The variability at time scales from 1 month to 15 years is interpreted as refractive interstellar scintillations in fast-moving nearby (less than 150 pc) hot gas, near shock waves in the LISM. An all-sky map of scintillation indices, m, averaged over three–five sources closest to one another, shows several m maxima. Two of the three most pronounced maxima are probably connected with Loop I; the third one coincides with the soft X-ray (0.1–0.3 keV) background maximum near the South Galactic Pole. Other, less certain, m maxima probably correspond to the Orion star-formation region and to a soft X-ray maximum near the North Galactic Pole. The ‘free-of-gas’ tunnel in the direction l=240° corresponds to low values of m. The estimated time scale of interstellar scintillations on the above-mentioned LISM structures is in agreement with that of the observed radio-source variations. 相似文献
19.
20.
Broten NW MacLeod JM Avery LW Irvine WM Hoglund B Friberg P Hjalmarson A 《The Astrophysical journal》1984,(1):L25-L29
A new interstellar molecule, methylcyanoacetylene (CH3C3N), has been detected in the molecular cloud TMC-1. The J = 8 --> 7, J = 7 --> 6, J = 6 --> 5, and J = 5 --> 4 transitions have been observed. For the first three of these, both the K = 0 and K = 1 components are present, while for J = 5 --> 4, only the K = 0 line has been detected. The observed frequencies were calculated by assuming a value of radial velocity VLSR = 5.8 km s-1 for TMC-1, typical of other molecules in the cloud. All observed frequencies are within 10 kHz of the calculated frequencies, which are based on the 1982 laboratory constants of Moises et al., so the identification is secure. The lines are broadened by hyperfine splitting, and the J = 5 --> 4, K = 0 transition shows incipient resolution into three hyperfine components. The rotational temperature determined for these observations is quite low, with 2.7 K < or = Trot < or = 4 K. the total column density is approximately 5 x 10(12) cm-2. 相似文献