| 1. |
- Ghosh, Rana, et al.
(author)
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Phenol in High-mass Star-forming Regions
- 2022
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In: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 22:6
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Journal article (peer-reviewed)abstract
- Phenol, which belongs to the C6H6O isomeric group, is the simplest molecule in the family of alcohol of the aromatic series. Although phenol has yet to be detected in the interstellar medium, a tentative identification was reported toward the Orion KL hot core using the IRAM-30 m line survey. To explore some more species of this isomeric group, we consider ten species to study the fate of their astronomical detection. It is noticed that phenol is the most energetically favorable isomer of this group. In contrast, propargyl ether is the least favorable (having relative energy similar to 103 kcal mol(-1) compared to phenol) species of this group. So far, the studies associated with the formation of phenol are heavily concentrated on combustion chemistry. Here, we suggest a few key reactions (C6H6 + OH -> C6H5 + H2O, C6H6 + O -> C6H5OH, C6H6 + H -> C6H5 + H-2, and C6H5 + OH -> C6H5OH + h nu) for the formation of phenol. All these pathways are included in a large gas-grain chemical network to study its formation in high mass star-forming regions and dark cloud environments. It is noticed that the phenyl (-C6H5) formation by the ice-phase hydrogen abstraction reaction of benzene (i.e., C6H6 + OH -> C6H5 + H2O if allowed at similar to 10 K) could serve as the starting point for the formation of phenol in the gas phase by radiative association reaction C6H5 + OH -> C6H5OH + h nu. The gas-phase reaction C6H6 + O -> C6H5OH significantly contributes to the formation of phenol, when the ice-phase reaction C6H6 + OH -> C6H5 + H2O is not considered at low temperature. Band 4 ALMA archival data of a hot molecular core, G10.47+0.03, are analyzed. It yields an upper limit on phenol abundance of 5.19 x 10(-9). Our astrochemical model delivers an upper limit on phenol abundance of similar to 2.20 x 10(-9) in the hot molecular core, whereas its production in the dark cloud is not satisfactory.
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| 2. |
- Sil, Milan, et al.
(author)
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Chemical Complexity of Phosphorous-bearing Species in Various Regions of the Interstellar Medium
- 2021
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 162:3
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Journal article (peer-reviewed)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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| 3. |
- Srivastav, Satyam, et al.
(author)
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Astrochemical model to study the abundances of branched carbon-chain molecules in a hot molecular core with realistic binding energies
- 2022
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 515:3, s. 3524-3538
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Journal article (peer-reviewed)abstract
- Straight-chain (normal-propyl cyanide, n - C3H7CN) and branched-chain (iso-propyl cyanide, i - C3H7CN) alkyl cyanides are recently identified in the massive star-forming regions (Sgr B2(N) and Orion). These branched-chain molecules indicate that the key amino acids (side-chain structures) may also be present in a similar region. The process by which this branching could propagate towards the higher order (butyl cyanide, C4H9CN) is an active field of research. Since the grain catalysis process could have formed a major portion of these species, considering a realistic set of binding energies are indeed essential. We employ quantum chemical calculations to estimate the binding energy of these species considering water as a substrate because water is the principal constituent of this interstellar ice. We find significantly lower binding energy values for these species than were previously used. It is noticed that the use of realistic binding energy values can significantly change the abundance of these species. The branching is more favourable for the higher order alkyl cyanides with the new binding energies. With the inclusion of our new binding energy values and one essential destruction reaction (i - C3H7CN + H -> CH3C(CH3)CN + H-2 , having an activation barrier of 947 K), abundances of t - C4H9CN dramatically increased.
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