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Park SM, Kwon CH. Conformational diversity and environmental implications of trans-2-pentenal. Phys Chem Chem Phys 2023; 25:28612-28620. [PMID: 37869992 DOI: 10.1039/d3cp04204a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2023]
Abstract
This study investigates the conformational intricacies of trans-2-pentenal (trans-2PA), a significant biogenic volatile organic compound. To unveil its potential implications in atmospheric chemistry and environmental pollution, we employ advanced infrared resonant vacuum ultraviolet mass-analysed threshold ionisation spectroscopy. Through this method, we identify the major conformers within trans-2PA, encompassing trans-s-trans (tt-) and trans-s-cis (tc-) structures with planar (cis) and non-planar (gauche) configurations introduced by a methyl group. In a pioneering spectroscopic examination, we analyze trans-2PA in both the neutral and cationic states. This approach allows us to gain a comprehensive understanding of its molecular behavior. Our conformer-specific vibrational spectra not only reveal the relative populations of the main conformers, notably tt-cis and tt-gauche conformers, but also shed light on atmospheric oxidation processes and lower tropospheric organic aerosol formation mechanisms. Our findings expand the understanding of the role of trans-2PA in environmental and biological contexts. Additionally, they contribute to a broader understanding of its influence on air quality, climate, and atmospheric dynamics. The collaboration between advanced experimental techniques and computational methods fortifies the scientific underpinning of this study, opening doors to further exploration in the realms of atmospheric chemistry and environmental science.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
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2
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Conformational Structures of Neutral and Cationic Pivaldehyde Revealed by IR-Resonant VUV-MATI Mass Spectroscopy. Int J Mol Sci 2022; 23:ijms232314777. [PMID: 36499105 PMCID: PMC9735833 DOI: 10.3390/ijms232314777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 11/22/2022] [Accepted: 11/23/2022] [Indexed: 11/29/2022] Open
Abstract
Pivaldehyde, which is an unwanted by-product released with engine exhaust, has received considerable research attention because of its hydrocarbon oxidations at atmospheric temperature. To gain insight into the conformer-specific reaction dynamics, we investigated the conformational structures of the pivaldehyde molecule in neutral (S0) and cationic (D0) states using the recently invented IR-resonant VUV-MATI mass spectroscopy. Additionally, we constructed the two-dimensional potential energy surfaces (2D PESs) associated with the conformational transformations in the S0 and D0 states to deduce the conformations corresponding to the measured vibrational spectra. The 2D PESs indicated the presence of only the eclipsed conformation in the global minima of both states, unlike those in propanal and isobutanal. However, comparing the IR-dip VUV-MATI spectra from two intense peaks in the VUV-MATI spectrum with the anharmonic IR simulations revealed the correspondence between the gauche conformer on the S0 state and the measured IR spectra. Furthermore, Franck-Condon analysis confirmed that most peaks in the VUV-MATI spectrum are attributed to the adiabatic ionic transitions between the neutral gauche and cationic eclipsed conformers in pivaldehyde. Consequently, electron removal from the highest occupied molecular orbital, consisting of the nonbonding orbital of the oxygen atom in pivaldehyde, promoted the formyl-relevant modes in the induced cationic eclipsed conformer.
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Park SM, Kwon CH. Identification of individual conformers in C 4H 6O isomers using conformer-specific vibrational spectroscopy. RSC Adv 2021; 11:38240-38246. [PMID: 35498109 PMCID: PMC9044234 DOI: 10.1039/d1ra07397d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 11/23/2021] [Indexed: 11/21/2022] Open
Abstract
We measured the conformer-specific vibrational spectra of C4H6O isomers in neutral and cationic states using IR resonant vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy for the first time. Notably, the measured IR dip and hole-burn VUV-MATI spectra for each isomer represent the identifiable vibrational spectra of individual conformers in both states. Furthermore, we estimated the relative populations of individual conformers in crotonaldehyde (CA) and methyl vinyl ketone (MVK) isomers using the IR dip intensity, the corresponding Franck-Condon factor, and the IR absorption cross section. Our analysis revealed that the compositional ratio of s-trans to s-cis conformers in the CA isomer remained at 95.8 : 4.2 even under supersonic expansion, whereas that in the MVK isomer was determined as 90.6 : 9.4, which is consistent with previous research. These findings reveal that the conformational stability of each isomer depends on the position of the methyl group relative to the carbonyl group.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University Chuncheon 24341 Korea
| | - Chan Ho Kwon
- Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University Chuncheon 24341 Korea
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Park SM, Kwon CH. Development and Verification of Conformer-Specific Vibrational Spectroscopy. J Phys Chem A 2021; 125:9251-9258. [PMID: 34628860 DOI: 10.1021/acs.jpca.1c07162] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Conformers have similar vibrational structures both in neutral (S0) and cationic (D0) states owing to the comparable force fields between their nuclei. Nevertheless, there is a continuous development of vibrational spectroscopic techniques to rigorously identify individual conformers in the designated molecule but only in the S0 state. We developed an inventive conformer-specific vibrational spectroscopic technique to measure identifiable vibrational spectra of individual conformers in both S0 and D0 states. We measured isomer-specific vibrational spectra in both states for gas-phase acetone and oxetane isomers from a solution with azeotropic composition to verify the proposed techniques that are based on infrared (IR) resonant vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. The measured IR dip VUV-MATI and IR hole-burn VUV-MATI spectra for each isomer, which correspond to isomer-specific vibrational spectra in both states, can be represented by IR-resonant VUV photoionization and one-photon VUV-MATI spectra of the binary mixture, respectively, under supersonic expansion conditions. The partial pressures of the individual isomers in the binary mixture with different mole fractions estimated according to the relative peak intensities in the measured spectra provide insights on solute-solvent interactions. We suggest that the verified IR-resonant VUV-MATI spectroscopy can form the basis of effective schemes toward conformational chemistry.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
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Lee YR, Kim MH, Kwon CH. Probing the Photoionization Dynamics of 2-Cyclopenten-1-one via High-Resolution VUV-MATI Spectroscopy. J Phys Chem A 2021; 125:2356-2363. [PMID: 33724025 DOI: 10.1021/acs.jpca.1c01093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
2-Cyclopenten-1-one (2CP), which is a cyclic enone, has been considered an important precursor because of its versatile functionality in the synthesis of natural products and materials for biofuels. Here, we report the adiabatic ionization energy (AIE) and cationic structure of 2CP in the ionic transition between the neutral S0 and the cationic D0 states probed by high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. From the 0-0 band position in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the AIE of 2CP was determined to be 9.3477 ± 0.0004 eV (75,395 ± 3 cm-1), which is in good agreement with the reference value but much more accurate. The measured MATI spectrum combined with the Franck-Condon fitting at the B3LYP/cc-pVTZ level revealed that the cationic structure of 2CP is twisted with the C1 symmetry, whereas the neutral 2CP has the CS symmetry. The results indicate that geometrical changes induced by ionization are mainly attributed to the electron removal from the highest occupied molecular orbital, which consists of nonbonding orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane of 2CP. Consequently, lowering the C1 symmetry for cationic 2CP led to the promotions of the ring-bending and ring-twisting modes in the MATI spectrum, which correspond to the ring puckering and C═C twisting in the S0 state, respectively.
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Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center, Ewha Womans University, Seoul 03760, South Korea
| | - Myung Hwa Kim
- Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 03760, South Korea
| | - Chan Ho Kwon
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
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Park SM, Choi J, Kim HL, Kwon CH. Conformer-specific VUV-MATI spectroscopy of methyl vinyl ketone: stabilities and cationic structures of the s- trans and s- cis conformers. Phys Chem Chem Phys 2020; 22:28383-28392. [PMID: 33300923 DOI: 10.1039/d0cp05782g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Methyl vinyl ketone (MVK), a volatile compound with photochemical activity, has received considerable attention in the fields of environmental chemistry and atmospheric chemistry. We explored the conformational stabilities of MVK in the neutral S0 and the cationic D0 states using conformer-specific vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy, which provided identifiable vibrational spectra for cationic MVK conformers. Based on the origin bands of the two individual conformers of MVK identified in the MATI spectra under different supersonic expansion conditions, the accurate adiabatic ionization energies of the s-trans and the s-cis conformers were determined to be 77 867 ± 4 (9.6543 ± 0.0005 eV) and 78 222 ± 4 cm-1 (9.6983 ± 0.0005 eV), respectively. The identifiable vibrational spectra of the two cationic conformers were further confirmed using vibrational assignments based on the Franck-Condon fit. Accordingly, precise cationic structures of the MVK conformers could be determined. The structural changes of the two conformers upon ionization could be attributed to the removal of an electron from the highest occupied molecular orbital of each conformer, which consists of nonbonding molecular orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane. Consequently, the s-trans conformer was preferred by 48 ± 18 and 403 ± 18 cm-1 in the neutral ground S0 and the cationic D0 states, respectively, which was supported by density-corrected density functional theory calculations and natural bond orbital analysis.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
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Eom SY, Lee YR, Kwon CH. Accurate conformational stability and cationic structure of piperidine determined by conformer-specific VUV-MATI spectroscopy. Phys Chem Chem Phys 2020; 22:22823-22832. [PMID: 33021609 DOI: 10.1039/d0cp04407e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Piperidine has received attention in pharmaceutical synthesis and biochemical degradation because of its conformational activity. We explored the conformational structures of piperidine in the neutral (S0) and cationic (D0) ground states by conformer-specific vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy, which provides high-resolution vibrational spectra for the corresponding cationic conformer. To identify conformers corresponding to the obtained VUV-MATI spectra, equilibrium structures of piperidine conformers in the S0 and D0 states were determined at various density functional theory levels, and potential energy surfaces associated with the conformational changes were constructed. Notably, the chair form interconverting between the equatorial NH and the axial NH conformers (Chair-Eq and Chair-Ax) in piperidine lies on the global minimum of the S0 state, but only the axial-like NH conformer (Chair-Ax-like) in chair form exists in the D0 state. The vibrational assignment of the observed spectra was accomplished through Franck-Condon (FC) analysis for adiabatic transitions between two Chair-Eq and Chair-Ax conformers and a cationic Chair-Ax-like conformer. Rigorous FC analysis revealed the precise structure of a cationic Chair-Ax-like conformer induced by removal of an electron from the lone-pair sp3 orbital of the nitrogen atom in piperidine. The adiabatic ionization energies of Chair-Eq and Chair-Ax conformers converting to a cationic state were determined to be 64 704 ± 4 cm-1 (8.0223 ± 0.0005 eV) and 64 473 ± 4 cm-1 (7.9936 ± 0.0005 eV), respectively. Consequently, the difference between their adiabatic ionization energies allowed the accurate determination of the conformational stability of Chair-Eq and Chair-Ax conformers in piperidine (231 ± 4 cm-1).
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Affiliation(s)
- So Young Eom
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
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Passos MO, Lins IA, Alves TV. Rate coefficients and product branching ratios for (E)-2-butenal + H reactions. Phys Chem Chem Phys 2020; 22:14246-14254. [PMID: 32555895 DOI: 10.1039/d0cp02142c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Thermal rate constants for the hydrogen abstraction reactions of (E)-2-butenal by hydrogen atoms were calculated, for the first time, using the multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT). After a torsional potential energy surface exploration, ten conformations of the transition states (including the mirror images) were found and separated into four conformational reaction channels (CRCs). Individual energy paths of each CRC were built, recrossing and quantum tunneling effects estimated, and the thermal rate constants obtained. Due to the hindered rotors, the torsional anharmonicity was incorporated in the rate coefficient through the calculations of the rovibrational partition functions using the extended two-dimensional torsional method (E2DT). For comparison, the one-well (1W-CVT/SCT) and harmonic multipath (MP-CVT/SCT) thermal rate constants were also estimated. In addition, kinetic Monte Carlo (KMC) simulations were performed to predict the product branching ratios. For all kinetic approaches, the formation of products of (R1) is predominant. Compared to the harmonic multipath estimation, the percentage of reaction (R4) increases by approximately 9% when the torsional anharmonicity is taken into account. For the reactions (R2) and (R3), the product branching ratio is slightly decreased when compared with the harmonic simulation.
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Affiliation(s)
- Maiara Oliveira Passos
- Departamento de Físico-Química, Instituto de Química - Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, Bahia, 40170-115, Brazil.
| | - Igor Araujo Lins
- Departamento de Físico-Química, Instituto de Química - Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, Bahia, 40170-115, Brazil.
| | - Tiago Vinicius Alves
- Departamento de Físico-Química, Instituto de Química - Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, Bahia, 40170-115, Brazil.
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Gu Z, Wang Y, Ren Y, Zhang B. Unraveling electronic states and relaxation dynamics in ultraviolet excited crotonaldehyde via femtosecond time-resolved photoelectron imaging. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2019.136918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Lee YR, Choi N, Kwon CH. Determination of the highest occupied molecular orbital and cationic structure of 2-chloropyridine by one-photon VUV-MATI spectroscopy and Franck–Condon fitting. Phys Chem Chem Phys 2020; 22:20858-20866. [DOI: 10.1039/d0cp03365k] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Substitution of a chlorine atom for the H in pyridine alters the HOMO of the molecule, which ultimately affects the cationic structure.
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Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center
- Ewha Womans University
- Seoul 03760
- Korea
| | - Nayoung Choi
- Department of Chemistry and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
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Lee YR, Kim MH, Kwon CH. Ring opening dissociation of cationic twisted conformer by conformer-specific cyclopentanone photoionization. J Chem Phys 2019; 151:164305. [DOI: 10.1063/1.5127233] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center, Ewha Womans University, Seoul 03760, South Korea
| | - Myung Hwa Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, South Korea
| | - Chan Ho Kwon
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
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Kang DW, Kim HL, Kwon CH. Conformational preference and cationic structure of 2-methylpyrazine by VUV-MATI spectroscopy and natural bond orbital analysis. Phys Chem Chem Phys 2019; 21:9255-9264. [DOI: 10.1039/c9cp00766k] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Alkylpyrazines, which are well-known as aromatic substances and traditional medicines, are interesting molecular systems, and their methyl conformations result in unique structural and dynamical properties.
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Affiliation(s)
- Do Won Kang
- Department of Chemistry
- College of Natural Sciences and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
| | - Hong Lae Kim
- Department of Chemistry
- College of Natural Sciences and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
| | - Chan Ho Kwon
- Department of Chemistry
- College of Natural Sciences and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
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