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Fischer I, Hemberger P. Photoelectron Photoion Coincidence Spectroscopy of Biradicals. Chemphyschem 2023; 24:e202300334. [PMID: 37325876 DOI: 10.1002/cphc.202300334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 06/15/2023] [Accepted: 06/15/2023] [Indexed: 06/17/2023]
Abstract
The electronic structure of biradicals is characterized by the presence of two unpaired electrons in degenerate or near-degenerate molecular orbitals. In particular, some of the most relevant species are highly reactive, difficult to generate cleanly and can only be studied in the gas phase or in matrices. Unveiling their electronic structure is, however, of paramount interest to understand their chemistry. Photoelectron photoion coincidence (PEPICO) spectroscopy is an excellent approach to explore the electronic states of biradicals, because it enables a direct correlation between the detected ions and electrons. This permits to extract unique vibrationally resolved photoion mass-selected threshold photoelectron spectra (ms-TPES) to obtain insight in the electronic structure of both the neutral and the cation. In this review we highlight most recent advances on the spectroscopy of biradicals and biradicaloids, utilizing PEPICO spectroscopy and vacuum ultraviolet (VUV) synchrotron radiation.
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Affiliation(s)
- Ingo Fischer
- Julius-Maximilians-Universität Würzburg, Institut für Physikalische und Theoretische Chemie, Am Hubland, D-97074, Würzburg, Germany
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institut (PSI), CH-5232, Villigen, Switzerland
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Schleier D, Gerlach M, Schaffner D, Mukhopadhyay DP, Hemberger P, Fischer I. Threshold photoelectron spectroscopy of trimethylborane and its pyrolysis products. Phys Chem Chem Phys 2023; 25:4511-4518. [PMID: 36445209 DOI: 10.1039/d2cp04513c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Trimethylborane (TMB) and its chemistry upon pyrolysis have been investigated by threshold photoelectron spectroscopy. TMB shows an unstructured spectrum and its adiabatic ionization energy (IEad) has been determined to be 9.93 ± 0.1 eV. Dissociative photoionization induces a methyl radical loss in TMB and the barrier to dissociation in the cation is measured to be 0.65 ± 0.1 eV. Upon pyrolysis methane loss dominates, leading to C2H5B, which can exist in five different isomeric structures. Quantum chemical calculations were used to investigate possible methane loss mechanisms as well as the isomerization pathways on the C2H5B potential energy surface. Through isomer-selective photoion mass-selected threshold photoelectron spectroscopy (ms-TPES) the two isomers CH3BCH2 and CH3CHBH were identified by their ms-TPE spectra and IEad values of 8.55 ± 0.02 eV and 8.73 ± 0.02 eV were determined, respectively. A second channel leading to the loss of ethene from TMB forms CH2BH, which exhibits an IEad value of 9.37 ± 0.03 eV. The reaction mechanism in the literature needs to be expanded by an additional methane loss from the intermediately formed ethyl methyl borane.
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Affiliation(s)
- Domenik Schleier
- Institute for Physical and Theoretical Chemistry, University of Würzburg, 97074, Würzburg, Germany.
| | - Marius Gerlach
- Institute for Physical and Theoretical Chemistry, University of Würzburg, 97074, Würzburg, Germany.
| | - Dorothee Schaffner
- Institute for Physical and Theoretical Chemistry, University of Würzburg, 97074, Würzburg, Germany.
| | - Deb Pratim Mukhopadhyay
- Institute for Physical and Theoretical Chemistry, University of Würzburg, 97074, Würzburg, Germany.
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute (PSI), 5232, Villigen, Switzerland.
| | - Ingo Fischer
- Institute for Physical and Theoretical Chemistry, University of Würzburg, 97074, Würzburg, Germany.
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Preitschopf T, Hirsch F, Lemmens AK, Rijs AM, Fischer I. The gas-phase infrared spectra of the 2-methylallyl radical and its high-temperature reaction products. Phys Chem Chem Phys 2022; 24:7682-7690. [PMID: 35302151 DOI: 10.1039/d2cp00400c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The resonance-stabilized 2-methylallyl radical, 2-MA, is considered as a possible intermediate in the formation of polycyclic aromatic hydrocarbons (PAHs) in combustion processes. In this work, we report on its contribution to molecular growth in a high-temperature microreactor and provide mass-selective IR/UV ion dip spectra of the radical, as well as the various jet-cooled reaction products, employing free electron laser radiation in the mid-infrared region. Small (aromatic) hydrocarbons such as fulvene, benzene, styrene, or para-xylene, as well as polycyclic molecules, like (methylated) naphthalene, were identified with the aid of ab initio DFT computations. Several reaction products differ by one or more methyl groups, suggesting that molecular growth is dominated by (de)methylation in the reactor.
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Affiliation(s)
- Tobias Preitschopf
- Institute of Physical and Theoretical Chemistry, University of Wuerzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Florian Hirsch
- Institute of Physical and Theoretical Chemistry, University of Wuerzburg, Am Hubland, 97074 Würzburg, Germany.
| | - Alexander K Lemmens
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands.
| | - Anouk M Rijs
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands.
| | - Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Wuerzburg, Am Hubland, 97074 Würzburg, Germany.
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Pekkanen TT, Timonen RS, Robertson SH, Lendvay G, Joshi SP, Reijonen TT, Eskola AJ. An experimental and computational study of the reaction between 2-methylallyl radicals and oxygen molecules: optimizing master equation parameters with trace fitting. Phys Chem Chem Phys 2022; 24:4729-4742. [PMID: 35142299 DOI: 10.1039/d1cp05591g] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We have investigated the reaction between 2-methylallyl radicals and oxygen molecules with experimental and computational methods. Kinetic experiments were conducted in a tubular laminar flow reactor using laser photolysis for radical production and photoionization mass spectrometry for detection. The reaction was investigated as a function of temperature (203-730 K) and pressure (0.2-9 torr) in helium and nitrogen bath gases. At low temperatures (T < 410 K), the reaction proceeds by a barrierless reaction to form 2-methylallylperoxyl. Equilibration of the peroxyl adduct and the reactants was observed between 350-410 K. Measurements were extended to even higher temperatures, up to 730 K, but no reaction could be observed. Master equation simulations of the reaction system were performed with the MESMER program. Kinetic parameters in the master equation model were optimized by direct fitting to time-resolved experimental 2-methylallyl traces. Trace fitting is a recently implemented novel feature in MESMER. The trace approach was compared with the more traditional approach where one uses experimental rate coefficients for parameter optimization. The optimized parameters yielded by the two approaches are very similar and do an excellent job at reproducing the experimental data. The optimized master equation model was then used to simulate the reaction under study over a wide temperature and pressure range, from 200 K and 0.01 bar to 1500 K and 100 bar. The simulations predict a small phenomenological rate coefficient under autoignition conditions; about 1 × 10-18 cm3 s-1 at 400 K and 5 × 10-16 cm3 s-1 at 1000 K. We provide modified Arrhenius expressions in PLOG format for the most important product channels to facilitate the use of our results in combustion models.
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Affiliation(s)
- Timo T Pekkanen
- Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
| | - Raimo S Timonen
- Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
| | | | - György Lendvay
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar Tudósok krt. 2., Budapest H-1117, Hungary
| | - Satya P Joshi
- Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
| | - Timo T Reijonen
- Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
| | - Arkke J Eskola
- Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
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Fischer I, Pratt ST. Photoelectron spectroscopy in molecular physical chemistry. Phys Chem Chem Phys 2022; 24:1944-1959. [PMID: 35023533 DOI: 10.1039/d1cp04984d] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Photoelectron spectroscopy has long been a powerful method in the toolbox of experimental physical chemistry and molecular physics. Recent improvements in coincidence methods, charged-particle imaging, and electron energy resolution have greatly expanded the variety of environments in which photoelectron spectroscopy can be applied, as well as the range of questions that can now be addressed. In this Perspectives Article, we focus on selected recent studies that highlight these advances and research areas. The topics include reactive intermediates and new thermochemical data, high-resolution comparisons of experiment and theory using methods based on pulsed-field ionisation (PFI), and the application of photoelectron spectroscopy as an analytical tool to monitor chemical reactions in complex environments, like model flames, catalytic or high-temperature reactors.
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Affiliation(s)
- Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
| | - Stephen T Pratt
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA.
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Pekkanen T, Valkai L, Joshi S, Lendvay G, Heinonen P, Timonen R, Eskola A. An Experimental and Computational Study of the Reaction between Pent-3-en-2-yl Radicals and Oxygen Molecules: Switching from Pure Stabilisation to Pure Decomposition with Increasing Temperature. Faraday Discuss 2022; 238:619-644. [DOI: 10.1039/d2fd00031h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have used laser-photolysis – photoionization mass spectrometry, quantum chemical calculations, and master equation simulations to investigate the kinetics of the reaction between (E/Z)-pent-3-en-2-yl (CH3CHCHCHCH3), a resonance-stabilised hydrocarbon radical, and...
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Gerlach M, Monninger S, Schleier D, Hemberger P, Goettel JT, Braunschweig H, Fischer I. Photoelectron Photoion Coincidence Spectroscopy of NCl 3 and NCl 2. Chemphyschem 2021; 22:2164-2167. [PMID: 34390518 PMCID: PMC8596423 DOI: 10.1002/cphc.202100537] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 08/10/2021] [Indexed: 12/02/2022]
Abstract
We investigate NCl3 and the NCl2 radical by photoelectron‐photoion coincidence spectroscopy using synchrotron radiation. The mass selected threshold photoelectron spectrum (ms‐TPES) of NCl3 is broad and unstructured due to the large geometry change. An ionization energy of 9.7±0.1 eV is estimated from the spectrum and supported by computations. NCl2 is generated by photolysis at 213 nm from NCl3 and its ms‐TPES shows an extended vibrational progression with a 90 meV spacing that is assigned to the symmetric N−Cl stretching mode in the cation. An adiabatic ionization energy of 9.94 ± 0.02 eV is determined.
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Affiliation(s)
- Marius Gerlach
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Sophie Monninger
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Domenik Schleier
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institut (PSI), 5232, Villigen, Switzerland
| | - James T Goettel
- Institute of Inorganic Chemistry and Institute for Sustainable Chemistry and Catalysis with Boron, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Holger Braunschweig
- Institute of Inorganic Chemistry and Institute for Sustainable Chemistry and Catalysis with Boron, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
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