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Wang P, Lin Q, Xiao C, Yang X, Liu K, Pan H. Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH 3, CH 2, and CH Fragments. J Phys Chem A 2024; 128:5273-5284. [PMID: 38946501 DOI: 10.1021/acs.jpca.4c01914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Under irradiation of a vacuum ultraviolet (VUV) photon, methane dissociates and yields multiple fragments. This photochemical behavior is not only of fundamental importance but also with wide-ranging implications in several branches of science. Despite that and numerous previous investigations, the product channel branching is still under debate, and the underlying dissociation mechanisms remain elusive. In this study, the photofragment imaging technique was exploited for the first time to map out the momentum and anisotropy parameter distributions of the CH3, CH2, and CH fragments at the 118 nm photolysis wavelength (10.48 eV photon energy). In conjunction with previously reported results of the H atom fragment at 121.6 nm (10.2 eV), a complete set of product channel branching in both two-body and three-body fragmentations is accurately determined. We concluded that extensive nonadiabatic transitions partake in the processes with two-body fragmentations accounting for more than 90% of overall photodissociation, for which the channel branching values for CH2 + H2 and CH3 + H are about 0.66 and 0.25, respectively. Careful kinematic analysis enables us to untangle the intertwined triple fragmentations into the CH2(X̃ 3B1 and ã 1A1) + H + H and CH(X2Π) + H + H2 channels and to evidence their underlying sequential (or stepwise) mechanisms. With the aid of electronic correlation and prior theoretical calculations of the potential energy surfaces, the most probable or dominant dissociation pathways are elucidated. Comparisons with fragmentary reports in the literature on various photochemical aspects are also documented, and discrepancies are clarified. This comprehensive study benchmarks the VUV photochemistry of methane and advances our understanding of this important process.
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Affiliation(s)
- Pengcheng Wang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Qiaosong Lin
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Chunlei Xiao
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
| | - Xueming Yang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, P. R. China
| | - Kopin Liu
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- Aerosol Science Research Center, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei 10617, Taiwan
| | - Huilin Pan
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China
- Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, P. R. China
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Galassi R, Contini C, Pucci M, Gambi E, Manca G. Odorant Monitoring in Natural Gas Pipelines Using Ultraviolet-Visible Spectroscopy. APPLIED SPECTROSCOPY 2021; 75:168-177. [PMID: 32880187 DOI: 10.1177/0003702820960737] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The remote, timely and in-field detection of sulfured additives in natural gas pipelines is a challenge for environmental, commercial and safety reasons. Moreover, the constant control of the level of odorants in a pipeline is required by law to prevent explosions and accidents. Currently, the detection of the most common odorants (THT = tetrahydrothiophane; TBM = tertiary butyl mercaptan) added to natural gas streams in pipelines is made in situ by using portable gas chromatography apparatuses. In this study, we report the analysis of the ultraviolet spectra obtained by a customized ultraviolet spectrophotometer, named Spectra, for the in-field detection of thiophane and tertiary butyl mercaptan. Spectra were conceived to accomplish the remote analysis of odorants in the pipelines of the natural gas stream through the adoption of technical solutions aimed to adapt a basic bench ultraviolet spectrophotometer to the in-field analysis of gases. The remotely controlled system acquires spectra continuously, performing the quantitative determination of odorants and catching systemic or accidental variations of the gaseous mixture in different sites of the pipeline. The analysis of the experimental spectra was carried out also through theoretical quantum mechanical approaches aimed to detect and to correctly assign the nature of the intrinsic electronic transitions of the two odorants, thiophane and tertiary butyl mercaptan, that cause the ultraviolet absorptions. So far, these theoretical aspects have never been studied before. The absorption maxima of thiophane and tertiary butyl mercaptan spectra were computationally simulated through the usage of selected molecular models with satisfactory results. The good matches between the experimental and theoretical datasets corroborate the reliability of the collected data. During the tests, unexpected pollutants and accidental malfunctions have been detected and also identified by Spectra, making this instrument suitable for many purposes.
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Affiliation(s)
- Rossana Galassi
- School of Science and Technology, Chemistry Division, University of Camerino, Camerino, Italy
| | | | | | - Ennio Gambi
- Dipartimento di Ingegneria dell'Informazione, Università Politecnica delle Marche, Ancona, Italy
| | - Gabriele Manca
- Istituto di Chimica dei Composti Organo-Metallici, ICCOM-CNR, Sesto Fiorentino, Italy
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Savchenko E, Khyzhniy I, Uyutnov S, Bludov M, Bondybey V. Nonstationary processes in matrix-isolated methane probed by optical and current emission spectroscopy. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.128803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Jones JR, Rouet FH, Lawler KV, Vecharynski E, Ibrahim KZ, Williams S, Abeln B, Yang C, McCurdy W, Haxton DJ, Li XS, Rescigno TN. An efficient basis set representation for calculating electrons in molecules. Mol Phys 2016. [DOI: 10.1080/00268976.2016.1176262] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Jeremiah R. Jones
- Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | | | - Keith V. Lawler
- Department of Chemistry, University of Nevada-Las Vegas, Las Vegas, NV, USA
| | - Eugene Vecharynski
- Computing Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Khaled Z. Ibrahim
- Computing Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Samuel Williams
- Computing Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Brant Abeln
- Department of Chemistry, University of California, Davis, Davis, CA, USA
- Ultrafast X-Ray Science Laboratory, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Chao Yang
- Computing Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - William McCurdy
- Department of Chemistry, University of California, Davis, Davis, CA, USA
- Ultrafast X-Ray Science Laboratory, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Daniel J. Haxton
- Ultrafast X-Ray Science Laboratory, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
- Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Xiaoye S. Li
- Computing Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Thomas N. Rescigno
- Chemical Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
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Gans B, Boyé-Péronne S, Broquier M, Delsaut M, Douin S, Fellows CE, Halvick P, Loison JC, Lucchese RR, Gauyacq D. Photolysis of methane revisited at 121.6 nm and at 118.2 nm: quantum yields of the primary products, measured by mass spectrometry. Phys Chem Chem Phys 2011; 13:8140-52. [DOI: 10.1039/c0cp02627a] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Ren J, Kaxiras E, Meng S. Optical properties of clusters and molecules from real-time time-dependent density functional theory using a self-consistent field. Mol Phys 2010. [DOI: 10.1080/00268976.2010.491489] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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