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Schaffner D, Juncker von Buchwald T, Karaev E, Alagia M, Richter R, Stranges S, Coriani S, Fischer I. The x-ray absorption spectrum of the tert-butyl radical: An experimental and computational investigation. J Chem Phys 2024; 161:034309. [PMID: 39017428 DOI: 10.1063/5.0216364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2024] [Accepted: 06/16/2024] [Indexed: 07/18/2024] Open
Abstract
We report the x-ray absorption spectrum (XAS) of the tert-butyl radical, C4H9. The radical was generated pyrolytically from azo-tert-butane, and the XAS of the pure radical was obtained by subtraction of spectra recorded at different temperatures. The bands in the XAS were assigned by ab initio calculations that are in very good agreement with the experimental data. The lowest energy signal in the XAS is assigned to the C1s electron transition from the central carbon atom to the singly occupied molecular orbital (SOMO), while higher transitions correspond to C1s excitations from terminal carbon atoms. Furthermore, we investigated the fragmentation of the radical following resonant C1s excitation by electron-ion-coincidence spectroscopy. Several fragmentation channels were identified. The C1s excitation of the terminal carbons is associated with a stronger fragmentation tendency compared to the lowest C1s excitation of the central carbon into the SOMO. For this core excited state, we still observe an intact parent ion, C4H9+, and a comparatively higher tendency to dissociate into CH3+ + C3H6+.
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Affiliation(s)
- Dorothee Schaffner
- Institute of Physical and Theoretical Chemistry, University of Würzburg, D-97074 Würzburg, Germany
| | | | - Emil Karaev
- Institute of Physical and Theoretical Chemistry, University of Würzburg, D-97074 Würzburg, Germany
| | - Michele Alagia
- CNR-Istituto Officina dei Materiali (IOM), Laboratorio TASC, 34149 Trieste, Italy
| | - Robert Richter
- Elettra-Sincrotrone Trieste, Area Science Park, I-34149 Basovizza, Trieste, Italy
| | - Stefano Stranges
- CNR-Istituto Officina dei Materiali (IOM), Laboratorio TASC, I-34149 Trieste, Italy
- Dipartimento di Chimica e Tecnologia dei Farmaci, Università degli Studi di Roma "La Sapienza," Piazzale Aldo Moro 5, I-00185 Rome, Italy
| | - Sonia Coriani
- DTU Chemistry, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
| | - Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, D-97074 Würzburg, Germany
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Ali MA. Ab initio rate coefficients for reactions of 2,5-dimethylhexyl isomers with O 2: temperature- and pressure-dependent branching ratios. Phys Chem Chem Phys 2021; 23:6225-6240. [PMID: 33687383 DOI: 10.1039/d0cp06562e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Chemical kinetics of O2-addition to alkyl radicals (R), termed first O2-addition in the oxidation mechanism of alkanes, are of central importance to next-generation combustion strategies designed for operations in the low- to intermediate-temperature region (<1000 K). In the present work, stationary points on potential energy surfaces (PES), temperature- and pressure-dependent rate coefficients, and branching fractions of product formation from R + O2 reactions initiated by the addition of molecular oxygen (3O2) to the three alkyl radicals of a branched alkane, 2,5-dimethylhexane, are reported. The stationary points were determined utilizing ab initio/DFT methods and the reaction energies were computed using the composite CBS-QB3 method. Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) calculations were employed to compute rate coefficients, from which branching fractions were determined over the pressure range of 10-3-20 atm and the temperature range of 400-900 K on three different surfaces. The quantum chemistry results reveal several distinct features. For the addition of O2 to the tertiary alkyl radical 2,5-dimethylhex-2-yl, the most energetically favorable channel leads to the formation of 2,2,5,5,-tetramethyl-tetrahydrofuran, a cyclic ether intermediate formed coincident with OH in a chain-propagating step from the decomposition of tertiary-tertiary hydroperoxyalkyl (QOOH). On the R + O2 surface of the secondary radical, 2,5-dimethylhex-3-yl, the pathways for the formation of methyl-propanal + iso-butene + OH via concerted C-C and O-O bond scission of tertiary QOOH and that of cyclic ether + OH are the most energetically favorable pathways. The R + O2 surface for the reaction of the primary radical, 2,5-dimethylhex-1-yl, reveals two competitive chain-propagation channels, leading to 2-iso-propyl-4-methyl-tetrahydrofuran + OH and 2,2,5-trimethyltetrahydropyran + OH. Below 100 Torr, the formation of the aforementioned species dominates the respective total R + O2 rate coefficient, while at pressures above 1 atm collisionally stabilized alkylperoxy (ROO) dominates at the temperatures considered here. The results of this study are in very good agreement with the experimentally measured intermediates and products of the 2,5-dimethylhexyl radical + O2 reaction.
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Affiliation(s)
- Mohamad Akbar Ali
- Department of Chemistry, College of Science, King Faisal University, Al-Ahsa 31982, Saudi Arabia.
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Whelan CA, Blitz MA, Shannon R, Onel L, Lockhart JP, Seakins PW, Stone D. Temperature and Pressure Dependent Kinetics of QOOH Decomposition and Reaction with O2: Experimental and Theoretical Investigations of QOOH Radicals Derived from Cl + (CH3)3COOH. J Phys Chem A 2019; 123:10254-10262. [DOI: 10.1021/acs.jpca.9b08785] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Mark A. Blitz
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - Robin Shannon
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - Lavinia Onel
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | | | - Paul W. Seakins
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - Daniel Stone
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
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Rhodes CJ. Radiolabelling Studies of Free Radicals Using Muonium (The Second Hydrogen Radioisotope). PROGRESS IN REACTION KINETICS AND MECHANISM 2019. [DOI: 10.3184/007967400103165146] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
An overview is presented of the way various spectroscopic/radioisotopic-labelling methods (MuSR), in which free radicals are labelled with the light hydrogen radioisotope muonium, may be employed in the study of free radical reaction kinetics and dynamics. Specifically considered are: the reaction rates of thiyl radicals and related species in relation to biological membrane damage; the dynamics of radicals sorbed in solid catalysts and in activated carbons and other porous particulate materials of environmental significance; reacting gas-phase systems; mechanisms for the formation of muon (muonium) labelled radicals, and the study of radical stabilisation and reactivity.
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Affiliation(s)
- Christopher J. Rhodes
- School of Pharmacy and Chemistry, Liverpool John Moores University, Byrom St., Liverpool L3 3AF, UK
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Snitsiriwat S, Bozzelli JW. Thermochemistry, Reaction Paths, and Kinetics on thetert-Isooctane Radical Reaction with O2. J Phys Chem A 2014; 118:4631-46. [DOI: 10.1021/jp502702f] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Suarwee Snitsiriwat
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102 United States
| | - Joseph W. Bozzelli
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102 United States
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Rhodes CJ. Muonium--the second radioisotope of hydrogen: a remarkable and unique radiotracer in the chemical, materials, biological and environmental sciences. Sci Prog 2012; 95:101-74. [PMID: 22893978 PMCID: PMC10365539 DOI: 10.3184/003685012x13336424471773] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Muonium (Mu), may be regarded as a radioactive hydrogen atom with a positive muon as its nucleus, and is formed in a range of media which are irradiated with positive muons. This exotic atom can be considered as a second radioisotope of hydrogen, along with tritium. Addition of this light atom (with a mass 1/9th that of a normal hydrogen, protium, atom) to unsaturated organic molecules forms free radicals, in which the muon serves as a radioactive and magnetic probe of their kinetic and structural properties. Suitable examples are chosen to illustrate the very large functionality of organic radicals which have been measured using muons and various methods of muSR, where mu stands for muon, S for spin and R may refer to rotation, resonance or relaxation. The principal techniques illustrated are transverse-field muon spin rotation (TF-muSR), avoided level crossing muon spin resonance (ALC-muSR) and longitudinal-field muon spin relaxation (LF-muSRx). Structural studies of radicals, the determination of mechanisms for radical formation, the measurement of radical stabilisation energies, the determination of the kinetics of reactions of free muonium atoms and of free radicals have all been accomplished using TF-muSR methods. It is further shown that TF-muSR is most useful in measuring radical reaction rates in non-aqueous media, to provide information of relevance to cell membrane damage and repair Muonium may further be used as a mechanistic probe since it determines a true pattern of H-atom reactivity in molecules, against which results from similar radiolysed materials may be compared. [In many solid materials that are exposed to ionising radiation, apparent H-atom adduct radicals are detected but which originate from charge-neutralisation of positive holes (radical cations) and ejected electrons, without free H-atoms being formed. DNA is the superlative example of this. Free H-atoms normally feature in the province of radiolysed aqueous media]. The applications of ALC-muSR and LF-muSRx in studying the reorientation of reactive radicals on reactive surfaces forms the substantive proportion of the review: considered specifically are radicals sorbed in zeolites, in clays and in porous silica, in porous carbons and on ice-surfaces, in connection with their role as intermediates in catalytic systems, particularly hydrocarbon cracking and oxidation processes, and in atmospheric aerosol chemistry. The formation of muonium and other muon species in cation-exchanged zeolite-X samples are also considered, according to the evidence of longitudinal field repolarisation measurements. Finally, mention is given of the use of muSR techniques for studying radicals in the gas-phase.
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Villano SM, Huynh LK, Carstensen HH, Dean AM. High-Pressure Rate Rules for Alkyl + O2 Reactions. 1. The Dissociation, Concerted Elimination, and Isomerization Channels of the Alkyl Peroxy Radical. J Phys Chem A 2011; 115:13425-42. [DOI: 10.1021/jp2079204] [Citation(s) in RCA: 191] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Stephanie M. Villano
- Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Lam K. Huynh
- International University, Vietnam National University − HCMC and Institute for Computational Science and Technology at HCMC, Vietnam
| | - Hans-Heinrich Carstensen
- Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Anthony M. Dean
- Chemical and Biological Engineering Department, Colorado School of Mines, Golden, Colorado 80401, United States
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Leitich J, Heise I, Angermund K, Rust J. The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals. European J Org Chem 2002. [DOI: 10.1002/1099-0690(200206)2002:11<1803::aid-ejoc1803>3.0.co;2-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Villenave E, Lesclaux R. Kinetic studies of the self-reaction and reaction with HO2 of a tertiary ?-brominated peroxy radical between 298 and 393 K. INT J CHEM KINET 2000. [DOI: 10.1002/1097-4601(20010101)33:1<41::aid-kin5>3.0.co;2-j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Dilger H, Stolmár M, Himmer U, Roduner E, Reid ID. Kinetics of the Gas-Phase Addition of the Ethyl Radical and the tert-Butyl Radical to NO. J Phys Chem A 1998. [DOI: 10.1021/jp981101a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Herbert Dilger
- Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Martina Stolmár
- Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Ulrich Himmer
- Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Emil Roduner
- Institut für Physikalische Chemie, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Ivan D. Reid
- Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
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