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McGuire BA, Martin-Drumel MA, Thorwirth S, Brünken S, Lattanzi V, Neill JL, Spezzano S, Yu Z, Zaleski DP, Remijan AJ, Pate BH, McCarthy MC. Molecular polymorphism: microwave spectra, equilibrium structures, and an astronomical investigation of the HNCS isomeric family. Phys Chem Chem Phys 2018; 18:22693-705. [PMID: 27478937 DOI: 10.1039/c6cp03871a] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry-Pérot Fourier-transform microwave spectroscopy between 6 and 40 GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35-37 kcal mol(-1) less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determined for the normal and rare isotopic species of both molecules; all are in good agreement with theoretical predictions obtained at the coupled cluster level of theory. On the basis of isotopic spectroscopy, precise molecular structures have been derived for all four isomers by correcting experimental rotational constants for the effects of rotation-vibration interaction calculated theoretically. Formation and isomerization pathways have also been investigated; the high abundance of HSCN relative to ground state HNCS, and the detection of strong lines of SH using CH3CN and H2S, suggest that HSCN is preferentially produced by the radical-radical reaction HS + CN. A radio astronomical search for HSCN and its isomers has been undertaken toward the high-mass star-forming region Sgr B2(N) in the Galactic Center with the 100 m Green Bank Telescope. While we find clear evidence for HSCN, only a tentative detection of HNCS is proposed, and there is no indication of HCNS or HSNC at the same rms noise level. HSCN, and tentatively HNCS, displays clear deviations from a single-excitation temperature model, suggesting weak masing may be occurring in some transitions in this source.
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Affiliation(s)
- Brett A McGuire
- National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903, USA and Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
| | | | - Sven Thorwirth
- I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - Sandra Brünken
- I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - Valerio Lattanzi
- Max-Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
| | - Justin L Neill
- Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904, USA
| | - Silvia Spezzano
- Max-Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
| | | | - Daniel P Zaleski
- Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904, USA
| | - Anthony J Remijan
- National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903, USA
| | - Brooks H Pate
- Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904, USA
| | - Michael C McCarthy
- National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903, USA and School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA.
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Nguyen HT, Hang TD, Nguyen MT. Theoretical Study of Silicon Monoxide Reactions with Ammonia and Methane. J Phys Chem A 2017; 121:1032-1040. [PMID: 28084737 DOI: 10.1021/acs.jpca.6b11665] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
High-accuracy calculations were performed to study the mechanisms of the reactions between the diatomic silicon monoxide (SiO) with NH3 and CH4. These reactions are relevant to the SiO-related astrochemistry and atmospheric chemistry as well as the activation of the N-H and C-H bonds by the SiO triple bond. Energetic data used in the construction of potential energy surfaces describing the SiO + NH3/CH4 reactions were obtained at the coupled-cluster theory with extrapolation to the complete basis set limit (CCSD(T)/CBS) using DFT/B3LYP/aug-cc-pVTZ optimized geometries. Standard heats of formation of a series of small Si-molecules were predicted. Insertion of SiO into the N-H bond is exothermic with a small energy barrier of ∼8 kcal/mol with respect to the SiO + NH3 reactants, whereas the C-H bond activation by SiO involves a higher energy barrier of 45 kcal/mol. Eight product channels are opened in the SiO + NH3 reaction including dehydrations giving HNSi/HSiN and dehydrogenations. These reactions are endothermic by 16-119 kcal/mol (calculated at 298.15 K) with the CCSD(T)/CBS energy barriers of 21-128 kcal/mol. The most stable set of products, HNSi + H2O, was also the product of the reaction pathway having lowest energy barrier of 21 kcal/mol. Ten product channels of the SiO + CH4 reaction including decarbonylation, dehydration, dehydrogenation, and formation of Si + CH3OH are endothermic by 19-118 kcal/mol with the energy barriers in the range of 71-126 kcal/mol. The formation of H2CSiO + H2O has the lowest energy barrier of 71 kcal/mol, whereas the most stable set of products, SiH4 + CO, is formed via a higher energy barrier of 90 kcal/mol. Accordingly, while SiO can break the N-H bond of ammonia without the assistance of other molecules, it is not able to break the C-H bond of methane.
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Affiliation(s)
- Huyen Thi Nguyen
- Computational Chemistry Research Group, Ton Duc Thang University , Ho Chi Minh City, 778000 Vietnam.,Faculty of Applied Sciences, Ton Duc Thang University , Ho Chi Minh City, 778000 Vietnam
| | - Tran Dieu Hang
- Department of Chemistry, KU Leuven , Celestijnenlaan 200F, B-3001 Leuven, Belgium
| | - Minh Tho Nguyen
- Computational Chemistry Research Group, Ton Duc Thang University , Ho Chi Minh City, 778000 Vietnam.,Faculty of Applied Sciences, Ton Duc Thang University , Ho Chi Minh City, 778000 Vietnam.,Department of Chemistry, KU Leuven , Celestijnenlaan 200F, B-3001 Leuven, Belgium
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5
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Raghunath P, Bhanuprakash K, Srinivas R. Formation of Silicon Analogues of Thio-isocyanic Acid, HNSiS, and Its Isomers by Neutral−Neutral Reactions of the Fragments: A Computational Study. J Phys Chem A 2004. [DOI: 10.1021/jp0478211] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- P. Raghunath
- Inorganic Chemistry Division, and National Centre for Mass Spectrometry, Indian Institute of Chemical Technology (IICT), Hyderabad-500 007, India
| | - K. Bhanuprakash
- Inorganic Chemistry Division, and National Centre for Mass Spectrometry, Indian Institute of Chemical Technology (IICT), Hyderabad-500 007, India
| | - R. Srinivas
- Inorganic Chemistry Division, and National Centre for Mass Spectrometry, Indian Institute of Chemical Technology (IICT), Hyderabad-500 007, India
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