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Karaev E, Gerlach M, Theil K, Garcia GA, Alcaraz C, Loison JC, Fischer I. Photoelectron spectrum of the pyridyl radical. Phys Chem Chem Phys 2024; 26:17042-17047. [PMID: 38836386 DOI: 10.1039/d4cp00688g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2024]
Abstract
We report the photoelectron spectrum of the pyridyl radical (C5H4N), a species of interest in astrochemistry and combustion. The radicals were produced via hydrogen abstraction in a fluorine discharge and ionized with synchrotron radiation. Mass-selected slow photoelectron spectra of the products were obtained from photoelectron-photoion coincidence spectra. A Franck-Condon simulation based on computed geometries and vibrational frequencies identified contributions of the o- and p-pyridyl radicals. For the o-isomer an adiabatic ionisation energy of 7.70 eV was obtained, in excellent agreement with a computed value of 7.72 eV. The spectrum of o-pyridyl is characterized by a long progression in an in-plane bending mode and the N-C stretch that contains the radical site.
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Affiliation(s)
- Emil Karaev
- University of Würzburg, Institute of Physical and Theoretical Chemistry, Am Hubland, 97074 Würzburg, Germany.
| | - Marius Gerlach
- University of Würzburg, Institute of Physical and Theoretical Chemistry, Am Hubland, 97074 Würzburg, Germany.
| | - Katharina Theil
- University of Würzburg, Institute of Physical and Theoretical Chemistry, Am Hubland, 97074 Würzburg, Germany.
| | - Gustavo A Garcia
- Synchrotron Soleil, L'Orme des Merisiers, St Aubin, B.P. 48, F-91192 Gif sur Yvette, France
| | - Christian Alcaraz
- Universite Paris-Saclay, CNRS, Institut de Chimie Physique, UMR8000, 91405 Orsay, France
| | | | - Ingo Fischer
- University of Würzburg, Institute of Physical and Theoretical Chemistry, Am Hubland, 97074 Würzburg, Germany.
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2
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Gupta D, Einholz R, Bettinger HF. Strain induced reactivity of cyclic iminoboranes: the (2 + 2) cycloaddition of a 1 H-1,3,2-diazaborepine with ethene. Chem Sci 2024; 15:666-674. [PMID: 38179531 PMCID: PMC10763563 DOI: 10.1039/d3sc04901a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Accepted: 11/19/2023] [Indexed: 01/06/2024] Open
Abstract
Iminoboranes have gathered immense attention due to their reactivity and potential applications as isoelectronic and isosteric alkynes. While cyclic alkynes are well investigated and useful reagents, cyclic iminoboranes are underexplored and their existence was inferred only via trapping experiments. We report the first direct spectroscopic evidence of a cyclic seven-membered iminoborane, 1-(tert-butyldimethylsilyl)-1H-1,3,2-diazaborepine 2, under cryogenic matrix isolation conditions. The amino-iminoborane 2 was photochemically generated in solid argon at 4 K from 2-azido-1-(tert-butyldimethylsilyl)-1,2-dihydro-1,2-azaborinine (3) and was characterized using FT-IR, UV-vis spectroscopy, and computational chemistry. The characteristic BN stretching vibration (1751 cm-1) is shifted by about 240 cm-1 compared to linear amino-iminoboranes indicating a significant weakening of the bond. The Lewis acidity value determined computationally (LAB = 9.1 ± 2.6) is similar to that of boron trichloride, and twelve orders of magnitude lower than that of 1,2-azaborinine (BN-aryne, LAB = 21.5 ± 2.6), a six-membered cyclic iminoborane. In contrast to the latter, the reduced ring strain of 2 precludes nitrogen fixation, but it unexpectedly allows facile (2 + 2) cycloaddition reaction with C2H4 under matrix isolation conditions at 30 K.
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Affiliation(s)
- Divanshu Gupta
- Institut für Organische Chemie, Universität Tübingen Auf der Morgenstelle 18 72076 Tübingen Germany
| | - Ralf Einholz
- Institut für Organische Chemie, Universität Tübingen Auf der Morgenstelle 18 72076 Tübingen Germany
| | - Holger F Bettinger
- Institut für Organische Chemie, Universität Tübingen Auf der Morgenstelle 18 72076 Tübingen Germany
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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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Chong D, Wang F. Dehydrogenation of Ammonia Borane Impacts Valence and Core Electrons: A Photoemission Spectroscopic Study. ACS OMEGA 2022; 7:35924-35932. [PMID: 36249405 PMCID: PMC9558250 DOI: 10.1021/acsomega.2c04632] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 08/24/2022] [Indexed: 06/16/2023]
Abstract
Ammonia borane (H3BNH3) is a promising material for hydrogen storage and release. Dehydrogenation of ammonia borane produces small boron-nitrogen hydrides such as aminoborane (H2BNH2) and iminoborane (HBNH). The present study investigates ammonia borane and its two dehydrogenated products for the first time using calculated photoemission spectra of the valence and core electrons. It is found that a significant decrease in the dipole moment was observed associated with the dehydration from 5.397 D in H3BNH3, to 1.942 D in H2BNH2, and to 0.083 D in HBNH. Such reduction in the dipole moment impacts properties such as hydrogen bonding, dihydrogen bonding, and their spectra. Dehydrogenation of H3BNH3 impacts both the valence and core electronic structure of the boron-nitrogen hydrides. The calculated valence vertical ionization energy (VIE) spectra of the boron-nitrogen hydrides show that valence orbitals dominated by 2p-electrons of B and N atoms exhibit large changes, whereas orbitals dominated by s-electrons, such as (3a14a15a1/3σ4σ5σ) remain less affected. The first ionization energy slightly increases from 10.57 eV for H3BNH3 to 11.29 eV for both unsaturated H2BNH2 and HBNH. In core space, the oxidative dehydrogenation of H3BNH3 affects the core electron binding energy (CEBE) of borane and nitrogen oppositely. The B1s binding energies increase from 194.01 eV in H3BNH3 to 196.93 eV in HBNH, up by 2.92 eV, whereas the N1s binding energies decrease from 408.20 eV in H3BNH3 to 404.88 eV in HBNH, dropped by 3.32 eV.
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Affiliation(s)
- Delano
P. Chong
- Department
of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Feng Wang
- Department
of Chemistry and Biotechnology, School of Science, Computing and Engineering
Technologies, Swinburne University of Technology, Melbourne, Victoria 3122, Australia
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Schleier D, Gerlach M, Pratim Mukhopadhyay D, Karaev E, Schaffner D, Hemberger P, Fischer I. Ammonia Borane, NH 3 BH 3 : A Threshold Photoelectron-Photoion Coincidence Study of a Potential Hydrogen-Storage Material. Chemistry 2022; 28:e202201378. [PMID: 35622451 PMCID: PMC9401591 DOI: 10.1002/chem.202201378] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Indexed: 12/17/2022]
Abstract
We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X+ 2E←X 1A1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE0K(NH3BH3, NH3BH2+)= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH3‐site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol−1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol−1.
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Affiliation(s)
- Domenik Schleier
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.,Present Address: Laboratory for Astrophysics, Leiden Observatory, Leiden University, 2300 RA, Leiden (The, Netherlands
| | - Marius Gerlach
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Deb Pratim Mukhopadhyay
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany.,Present address: Department of Dynamics of Molecules and Clusters, J. Heyrovský Institute of Physical Chemistry, Dolejškova 2155/3, 182 23, Praha 8, Czech Republic
| | - Emil Karaev
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
| | - Dorothee Schaffner
- 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
| | - Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, 97074, Würzburg, Germany
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Hemberger P, Wu X, Pan Z, Bodi A. Continuous Pyrolysis Microreactors: Hot Sources with Little Cooling? New Insights Utilizing Cation Velocity Map Imaging and Threshold Photoelectron Spectroscopy. J Phys Chem A 2022; 126:2196-2210. [PMID: 35316066 DOI: 10.1021/acs.jpca.2c00766] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Resistively heated silicon carbide microreactors are widely applied as continuous sources to selectively prepare elusive and reactive intermediates with astrochemical, catalytic, or combustion relevance to measure their photoelectron spectrum. These reactors also provide deep mechanistic insights into uni- and bimolecular chemistry. However, the sampling conditions and effects have not been fully characterized. We use cation velocity map imaging to measure the velocity distribution of the molecular beam signal and to quantify the scattered, rethermalized background sample. Although translational cooling is efficient in the adiabatic expansion from the reactor, the breakdown diagrams of methane and chlorobenzene confirm that the molecular beam component exhibits a rovibrational temperature comparable with that of the reactor. Thus, rovibrational cooling is practically absent in the expansion from the microreactor. The high rovibrational temperature also affects the threshold photoelectron spectrum of both benzene and the allyl radical in the molecular beam, but to different degrees. While the extreme broadening of the benzene TPES suggests a complex ionization mechanism, the allyl TPES is in fact consistent with an internal temperature close to that of the reactor. The background, room-temperature spectra of both are superbly reproduced by Franck-Condon simulations at 300 K. On the one hand, this leads us to suggest that room-temperature reference spectra should be used in species identification. On the other hand, analysis of the allyl iodide pyrolysis data shows that iodine atoms often recombine to form molecular iodine on the chamber surfaces. Such sampling effects may distort the chemical composition of the scattered background with respect to the molecular beam signal emanating directly from the reactor. This must be considered in quantitative analyses and kinetic modeling.
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Affiliation(s)
- Patrick Hemberger
- Paul Scherrer Insitute, Forschungsstrasse 111, CH-5232 Villigen PSI, Switzerland
| | - Xiangkun Wu
- Paul Scherrer Insitute, Forschungsstrasse 111, CH-5232 Villigen PSI, Switzerland
| | - Zeyou Pan
- Paul Scherrer Insitute, Forschungsstrasse 111, CH-5232 Villigen PSI, Switzerland
| | - Andras Bodi
- Paul Scherrer Insitute, Forschungsstrasse 111, CH-5232 Villigen PSI, Switzerland
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