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Chen Y, Wu X, Zhou X, Yang X, Dai X, Liu S. The N + Formation Mechanism of Vibrationally Selected N 2O + Ions in the C 2Σ + State: A TPEPICO Imaging Study. J Phys Chem A 2024; 128:4439-4447. [PMID: 38780798 DOI: 10.1021/acs.jpca.4c00494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2024]
Abstract
The N-NO bond fission of N2O+(C2Σ+) ions can produce two major fragment ions, NO+ or N+. In contrast to the dominant NO+ fragment ion, the N+ formation mechanism remains unclear to date. Here, dissociative photoionization of N2O via the C2Σ+ ionic state has been reinvestigated using a combined approach of threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging and quantum chemical calculations. Accompanying the N+(3P) formation, the NO(X2Π) neutral fragment with low and high vi-rotational distributions was identified, based on the N+ speed and angular distributions derived from the TPEPICO images. In particular, the excitation of the symmetric stretching ν1+ mode promotes the formation of high rotational components, while the asymmetric stretching ν3+ mode shows the exact opposite effect. According to our calculated multistate potential energy surfaces, intersystem crossing from C2Σ+ to 14Π exclusively provides feasible decomposition pathways to produce the N+ fragment. In a slightly bent geometry, spin-orbit couplings between C2Σ+ and two substates of 14Π, 14A' or 14A″, play a crucial role in the N+ formation from vibrationally selected N2O+(C2Σ+) ions. The mechanism also provides new insights into the charge transfer reaction of N+ + NO → N + NO+.
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Affiliation(s)
- Yan Chen
- Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xiangkun Wu
- Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xiaoguo Zhou
- Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
| | - Xinlang Yang
- Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xinhua Dai
- National Institute of Metrology, Beijing 100013, China
| | - Shilin Liu
- Hefei National Research Center for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
- Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China
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Wu X, Zhou X, Bjelić S, Hemberger P, Sztáray B, Bodi A. A plethora of isomerization processes and hydrogen scrambling in the fragmentation of the methanol dimer cation: a PEPICO study. Phys Chem Chem Phys 2022; 24:1437-1446. [PMID: 34984425 DOI: 10.1039/d1cp05155e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The valence photoionization of light and deuterated methanol dimers was studied by imaging photoelectron photoion coincidence spectroscopy in the 10.00-10.35 eV photon energy range. Methanol clusters were generated in a rich methanol beam in nitrogen after expansion into vacuum. They generally photoionize dissociatively to protonated methanol cluster cations, (CH3OH)nH+. However, the stable dimer parent ion (CH3OH)2+ is readily detected below the dissociation threshold to yield the dominant CH3OH2+ fragment ion. In addition to protonated methanol, we could also detect the water- and methyl-loss fragment ions of the methanol dimer cation for the first time. These newly revealed fragmentation channels are slow and cannot compete with protonated methanol cation formation at higher internal energies. In fact, the water- and methyl-loss fragment ions appear together and disappear at a ca. 150 meV higher energy in the breakdown diagram. Experiments with selectively deuterated methanol samples showed H scrambling involving two hydroxyl and one methyl hydrogens prior to protonated methanol formation. These insights guided the potential energy surface exploration to rationalize the dissociative photoionization mechanism. The potential energy surface was further validated by a statistical model including isotope effects to fit the experiment for the light and the perdeuterated methanol dimers simultaneously. The (CH3OH)2+ parent ion dissociates via five parallel channels at low internal energies. The loss of both CH2OH and CH3O neutral fragments leads to protonated methanol. However, the latter, direct dissociation channel is energetically forbidden at low energies. Instead, an isomerization transition state is followed by proton transfer from a methyl group, which leads to the CH3(H)OH+⋯CH2OH ion, the precursor to the CH2OH-, H2O-, and CH3-loss fragments after further isomerization steps, in part by a roaming mechanism. Water loss yields the ethanol cation, and two paths are proposed to account for m/z 49 fragment ions after CH3 loss. The roaming pathways are quickly outcompeted by hydrogen bond breaking to yield CH3OH2+, which explains the dominance of the protonated methanol fragment ion in the mass spectrum.
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Affiliation(s)
- Xiangkun Wu
- Paul Scherrer Institute, 5232 Villigen, Switzerland.
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Saša Bjelić
- Paul Scherrer Institute, 5232 Villigen, Switzerland.
| | | | - Bálint Sztáray
- University of the Pacific, Department of Chemistry, Stockton, CA 95211, USA
| | - Andras Bodi
- Paul Scherrer Institute, 5232 Villigen, Switzerland.
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Ionization energy and thermochemistry of CF2Cl2 determined from threshold photoelectron spectroscopy. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2021.138631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Wu X, Zhou X, Bjelić S, Hemberger P, Bodi A. Valence Photoionization and Energetics of Vanillin, a Sustainable Feedstock Candidate. J Phys Chem A 2021; 125:3327-3340. [PMID: 33872037 DOI: 10.1021/acs.jpca.1c00876] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We studied the valence photoionization of vanillin by photoelectron photoion coincidence spectroscopy in the 8.20-19.80 eV photon energy range. Vertical ionization energies by EOM-IP-CCSD calculations reproduce the photoelectron spectral features. Composite method calculations and Franck-Condon simulation of the weak, ground-state band yield the adiabatic ionization energy of the most stable vanillin conformer as 8.306(20) eV. The lowest energy dissociative photoionization channels correspond to hydrogen atom, carbon monoxide, and methyl losses, which form the dominant C8H7O3+ (m/z 151) and the less intense C7H8O2+ (m/z 124) and C7H5O3+ (m/z 137) fragment ions in parallel dissociation channels at modeled 0 K appearance energies of 10.13(1), 10.40(3), and 10.58(10) eV, respectively. On the basis of the breakdown diagram, we explore the energetics of sequential methyl and carbon monoxide loss channels, which dominate the fragmentation mechanism at higher photon energies. The 0 K appearance energy for sequential CO loss from the m/z 151 fragment to C7H7O2+ (m/z 123) is 12.99(10) eV, and for sequential CH3 loss from the m/z 123 fragment to C6H4O2+ (m/z 108), it is 15.40(20) eV based on the model. Finally, we review the thermochemistry of the bi- and trifunctionalized benzene derivatives guaiacol, hydroxybenzaldehyde, anisaldehyde, and vanillin. On the basis of isodesmic functional group exchange reactions, we propose new enthalpies of formations, among them ΔfH°298K(vanillin, g) = -383.5 ± 2.9 kJ mol-1. These mechanistic insights and ab initio thermochemistry results will support analytical works to study lignin conversion involving vanillin.
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Affiliation(s)
- Xiangkun Wu
- Paul Scherrer Institute, 5232 Villigen, Switzerland.,Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Saša Bjelić
- Paul Scherrer Institute, 5232 Villigen, Switzerland
| | | | - Andras Bodi
- Paul Scherrer Institute, 5232 Villigen, Switzerland
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Wu X, Zhou X, Hemberger P, Bodi A. Dissociative Photoionization of Chloro-, Bromo-, and Iodocyclohexane: Thermochemistry and the Weak C–Br Bond in the Cation. J Phys Chem A 2021; 125:646-656. [DOI: 10.1021/acs.jpca.0c10386] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiangkun Wu
- Paul Scherrer Institute, Villigen 5232, Switzerland
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | | | - Andras Bodi
- Paul Scherrer Institute, Villigen 5232, Switzerland
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Wu X, Zhou X, Hemberger P, Bodi A. Conformers, electronic states, and diabolical conical intersections in the valence photoelectron spectroscopy of halocyclohexanes. J Chem Phys 2020; 153:054305. [DOI: 10.1063/5.0018293] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Xiangkun Wu
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
| | - Andras Bodi
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
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Wu X, Zhou X, Hemberger P, Bodi A. A guinea pig for conformer selectivity and mechanistic insights into dissociative ionization by photoelectron photoion coincidence: fluorocyclohexane. Phys Chem Chem Phys 2020; 22:2351-2360. [PMID: 31934711 DOI: 10.1039/c9cp05617c] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We studied fluorocyclohexane (C6H11F, FC6) by double imaging photoelectron photoion coincidence spectroscopy in the 9.90-13.90 eV photon energy range. The photoelectron spectrum can identify species isomer and, in this case, even conformer selectively. Ab initio results indicated that the axial conformer has two, close-lying cation electronic states. With the help of Franck-Condon simulations of the vibrational fine structure, we determined the origin of three transitions, (i) axial FC6 → axial FC6+ of C1 symmetry (X[combining tilde]+, A'' in CS), (ii) equatorial FC6 → equatorial FC6+ of C1 symmetry (X[combining tilde]+, A'' in CS), and (iii) axial FC6 → A' axial FC6+ of CS symmetry (Ã+) as 10.12 ± 0.01, 10.15 ± 0.01 and 10.15 ± 0.02 eV, respectively. At slightly higher energies, the FC6 cation starts fragmenting by HF loss (E0 = 10.60 eV), followed by sequential CH3 (E0 = 10.71 eV) or C2H4 (E0 = 11.06 eV) loss. Surprisingly, the methyl-loss step has an effective barrier of only 0.11 eV, and yet it is a slow process at threshold. Based on the statistical model, this is explained by isomerization and stabilization of the C6H10+ intermediate. The highest energy channel observed, vinyl fluoride (C2H3F) loss yielding C4H8+ appears in the breakdown diagram at 12 eV, which agrees with the computed threshold to cyclobutane cation formation. However, the model predicted a ca. 1 eV competitive shift for this parallel channel, i.e., an E0 = 11.23 eV. This led us to explore the potential energy surface to find a lower-lying fragmentation channel including H-transfer steps. Rate constant measurements and statistical modeling thus yield fundamental insights into the reaction mechanism beyond what is immediately seen in the mass spectra.
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Affiliation(s)
- Xiangkun Wu
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland. and Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
| | - Andras Bodi
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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Chen Y, Yu T, Wu X, Zhou X, Liu S, Liu F, Dai X. C–F and C–H bond cleavage mechanisms of trifluoromethane ions in low-lying electronic states: threshold photoelectron–photoion coincidence imaging and theoretical investigations. Phys Chem Chem Phys 2020; 22:13808-13817. [DOI: 10.1039/d0cp01793k] [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
Dissociative ionization of trifluoromethane (CHF3) is investigated in the 13.9–18.0 eV energy range using the threshold photoelectron–photoion coincidence (TPEPICO) technique coupled to a vacuum ultraviolet synchrotron radiation source.
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Affiliation(s)
- Yan Chen
- National Institute of Metrology
- Beijing 100013
- China
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
| | - Tongpo Yu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Xiangkun Wu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Shilin Liu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Fuyi Liu
- National Synchrotron Radiation Laboratory
- University of Science and Technology of China
- Hefei 230029
- China
| | - Xinhua Dai
- National Institute of Metrology
- Beijing 100013
- China
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