| 1. |
- Das, Ankan, et al.
(författare)
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Effect of Binding Energies on the Encounter Desorption
- 2021
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media SA. - 2296-987X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The abundance of interstellar ice constituents is usually expressed with respect to the water ice because, in denser regions, a significant portion of the interstellar grain surface would be covered by water ice. The binding energy (BE) or adsorption energy of the interstellar species regulates the chemical complexity of the interstellar grain mantle. Due to the high abundance of water ice, the BE of surface species with the water is usually provided and widely used in astrochemical modeling. However, the hydrogen molecules would cover some part of the grain mantle in the denser and colder part of the interstellar medium. Even at around similar to 10 K, few atoms and simple molecules with lower adsorption energies can migrate through the surface. The BE of the surface species with H-2 substrate would be very different from that of a water substrate. However, adequate information regarding these differences is lacking. Here, we employ the quantum chemical calculation to provide the BE of 95 interstellar species with H-2 substrate. These are representative of the BEs of species to a H-2 overlayer on a grain surface. On average, we notice that the BE with the H-2 monomer substrate is almost ten times lower than the BE of these species reported earlier with the H2O c-tetramer configuration. The encounter desorption of H and H-2 was introduced [with E-D (H, H-2) = 45 K and E-D (H-2, H-2) = 23 K] to have a realistic estimation of the abundances of the surface species in the colder and denser region. Our quantum chemical calculations yield higher adsorption energy of H-2 than that of H [E-D (H, H-2) = 23-25 K and E-D (H-2, H-2) = 67-79 K]. We further implement an astrochemical model to study the effect of encounter desorption with the present realistic estimation. The encounter desorption of the N atom [calculations yield E-D (N, H-2) = 83 K] is introduced to study the differences with its inclusion.
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| 2. |
- Gorai, Prasanta, 1991, et al.
(författare)
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Identification of Methyl Isocyanate and Other Complex Organic Molecules in a Hot Molecular Core, G31.41+0.31
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 907:2
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Tidskriftsartikel (refereegranskat)abstract
- G31.41+0.31 is a well known chemically rich hot molecular core (HMC). Using Band 3 observations from the Atacama Large Millimeter Array (ALMA), we have analyzed the chemical and physical properties of the source. We have identified methyl isocyanate (CH3NCO), a precursor of prebiotic molecules, toward the source. In addition to this, we have reported the presence of complex organic molecules (COMs) like methanol (CH3OH), methanethiol (CH3SH), and methyl formate (CH3OCHO). Additionally, we have used transitions from molecules like HCN, (HCO+)-C-13, and SiO to trace the presence of infall and outflow signatures around the star-forming region. For the COMs, we have estimated the column densities and kinetic temperatures, assuming molecular excitation under local thermodynamic equilibrium (LTE) conditions. From the estimated kinetic temperatures of certain COMs, we found that multiple temperature components may be present in the HMC environment. Comparing the obtained molecular column densities between the existing observational results around other HMCs, it seems that the COMs are favorably produced in the hot core environment (similar to 100 K or higher). Though the spectral emissions toward G31.41+0.31 are not fully resolved, we find that CH3NCO and other COMs are possibly formed on grain/ice phase and populate the gas environment similar to other hot cores like Sgr B2, Orion KL, and G10.47+0.03.
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| 3. |
- Mondal, Suman Kumar, et al.
(författare)
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Is There Any Linkage between Interstellar Aldehyde and Alcohol?
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 922:2
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Tidskriftsartikel (refereegranskat)abstract
- It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA cycle 4 data of a hot molecular core, G10.47+0.03, are utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and column densities of these species were derived via the rotation diagram method assuming local thermodynamic equilibrium conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde-alcohol are considered for this study: (i) methanal and methanol, (ii) ethanal and ethanol, (iii) propanal and 1-propanol, (iv) propenal and allyl alcohol, (v) propynal and propargyl alcohol, and (vi) glycolaldehyde and ethylene glycol. One pair of ketone-alcohol (acetone and isopropanol) and ketene-alcohol (ethenone and vinyl alcohol) are also considered. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice-phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.
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| 4. |
- Sil, Milan, et al.
(författare)
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Chemical Complexity of Phosphorous-bearing Species in Various Regions of the Interstellar Medium
- 2021
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 162:3
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus-related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this paper, we carry out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos. We notice a curious correlation between the abundances of PO and PN and atomic nitrogen. Since N atoms are more abundant in diffuse clouds and PDRs than in the hot core/corino region, PO/PN reflects <1 in diffuse clouds, MUCH LESS-THAN1 in PDRs, and >1 in the late warm-up evolutionary stage of the hot core/corino regions. During the end of the post-warm-up stage, we obtain PO/PN > 1 for hot core and <1 for its low-mass analog. We employ a radiative transfer model to investigate the transitions of some of the P-bearing species in diffuse cloud and hot core regions and estimate the line profiles. Our study estimates the required integration time to observe these transitions with ground-based and space-based telescopes. We also carry out quantum chemical computation of the infrared features of PH3, along with various impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes around similar to 1000-1100 cm(-1). We also find that the presence of CO2 can strongly influence the intensity of the stretching modes around similar to 2400 cm(-1) of PH3.
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