1
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Ashworth EK, Ashworth SH, Bull JN. Spectroscopy and dynamics of isolated anions: Versatile instrumentation for photodetachment and photoelectron spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:075103. [PMID: 38984887 DOI: 10.1063/5.0207759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Accepted: 06/19/2024] [Indexed: 07/11/2024]
Abstract
Molecular anions are appealing targets for study because, compared with their neutral and cationic counterparts, they can be probed with conventional laboratory lasers without the need for multiphoton ionization schemes, and they provide spectroscopic details on the corresponding neutral molecules. Here, we describe a section of a modular instrument designed to perform high-throughput photoelectron and photodetachment spectroscopy of gas-phase anions, with future provision for time-resolved and isomer-selective spectroscopy. The instrument framework allows for the incorporation and adaptation of several ion sources, as demonstrated here with plasma (electric) discharge sources providing variable hard to soft ion generation conditions. The generated anions are separated according to their mass-to-charge ratio through time-of-flight mass spectrometry (m/zΔm/z = 500-600) and are focused into a set of perpendicular velocity-map imaging electrodes (ΔEE≈4%), where mass-selected anions are probed using laser light and the ejected electrons are velocity-map imaged. Instrument performance is demonstrated through the acquisition of photodetachment and photoelectron spectra for CH2CN-, showing sharp resonances in the vicinity of the detachment threshold assigned to rovibrational states of a dipole-bound anion and broader lifetime-limited spectral features at photon energies well above the threshold assigned to prompt autodetachment from a temporary anion resonance. Similar measurements could be performed on any molecular anions generated in the sources.
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Affiliation(s)
- Eleanor K Ashworth
- School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - Stephen H Ashworth
- School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - James N Bull
- School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom
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2
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Khatymov RV, Muftakhov MV, Tuktarov RF, Shchukin PV, Khatymova LZ, Pancras E, Terentyev AG, Petrov NI. Resonant electron capture by polycyclic aromatic hydrocarbon molecules: Effects of aza-substitution. J Chem Phys 2024; 160:124310. [PMID: 38533882 DOI: 10.1063/5.0195316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Accepted: 03/07/2024] [Indexed: 03/28/2024] Open
Abstract
Resonant electron capture by aza and diaza derivatives of phenanthrene (7,8-benzoquinoline and 1,10-phenanthroline) and anthracene (acridine and phenazine) at incident free electron energies (Ee) in the range of 0-15 eV was studied. All compounds except 7,8-benzoquinoline form long-lived molecular ions (M-) at thermal electron energies (Ee ∼ 0 eV). Acridine and phenazine also form such ions at epithermal electron energies up to Ee = 1.5-2.5 eV. The lifetimes (τa) of M- with respect to electron autodetachment are proportional to the extent of aza-substitution and increase on going from molecules with bent geometry of the fused rings (azaphenanthrenes) to linear isomers (azaanthracenes). These regularities are due to an increase in the adiabatic electron affinities (EAa) of the molecules. The EAa values of the molecules under study were comprehensively assessed based on a comparative analysis of the measured τa values using the Rice-Ramsperger-Kassel-Marcus theory, the electronic structure analysis using the molecular orbital approach, as well as the density functional calculations of the total energy differences between the molecules and anions. The only fragmentation channel of M- ions from the compounds studied is abstraction of hydrogen atoms. When studying [M-H]- ions, electron autodetachment processes were observed, the τa values were measured, and the appearance energies were determined. A comparative analysis of the gas-phase acidity of the molecules and the EAa values of the [M-H]· radicals revealed their proportionality to the EAa values of the parent molecules.
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Affiliation(s)
- Rustem V Khatymov
- Mendeleev University of Chemical Technology of Russia, Miusskaya Square, 9, 125047 Moscow, Russia
| | - Mars V Muftakhov
- Institute of Molecule and Crystal Physics, Ufa Federal Research Center, Russian Academy of Sciences, Prospekt Oktyabrya, 151, 450075 Ufa, Russia
| | - Renat F Tuktarov
- Institute of Molecule and Crystal Physics, Ufa Federal Research Center, Russian Academy of Sciences, Prospekt Oktyabrya, 151, 450075 Ufa, Russia
| | - Pavel V Shchukin
- Institute of Molecule and Crystal Physics, Ufa Federal Research Center, Russian Academy of Sciences, Prospekt Oktyabrya, 151, 450075 Ufa, Russia
| | - Lyaysan Z Khatymova
- Institute of Molecule and Crystal Physics, Ufa Federal Research Center, Russian Academy of Sciences, Prospekt Oktyabrya, 151, 450075 Ufa, Russia
| | - Eugene Pancras
- Ufa State Petroleum Technological University, ul. Kosmonavtov, 1, 450064 Ufa, Russia
| | - Andrey G Terentyev
- Mendeleev University of Chemical Technology of Russia, Miusskaya Square, 9, 125047 Moscow, Russia
| | - Nikolay I Petrov
- Mendeleev University of Chemical Technology of Russia, Miusskaya Square, 9, 125047 Moscow, Russia
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3
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Ranković M, Nag P, Anstöter CS, Mensa-Bonsu G, Kumar T P R, Verlet JRR, Fedor J. Resonances in nitrobenzene probed by the electron attachment to neutral and by the photodetachment from anion. J Chem Phys 2022; 157:064302. [PMID: 35963718 DOI: 10.1063/5.0101358] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We probe resonances (transient anions) in nitrobenzene with the focus on the electron emission from these. Experimentally, we populate resonances in two ways: either by the impact of free electrons on the neutral molecule or by the photoexcitation of the bound molecular anion. These two excitation means lead to transient anions in different initial geometries. In both cases, the anions decay by electron emission and we record the electron spectra. Several types of emission are recognized, differing by the way in which the resulting molecule is vibrationally excited. In the excitation of specific vibrational modes, distinctly different modes are visible in electron collision and photodetachment experiments. The unspecific vibrational excitation, which leads to the emission of thermal electrons following the internal vibrational redistribution, shows similar features in both experiments. A model for the thermal emission based on a detailed balance principle agrees with the experimental findings very well. Finally, a similar behavior in the two experiments is also observed for a third type of electron emission, the vibrational autodetachment, which yields electrons with constant final energies over a broad range of excitation energies. The entrance channels for the vibrational autodetachment are examined in detail, and they point to a new mechanism involving a reverse valence to non-valence internal conversion.
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Affiliation(s)
- Miloš Ranković
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
| | - Pamir Nag
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
| | - Cate S Anstöter
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Golda Mensa-Bonsu
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Ragesh Kumar T P
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Juraj Fedor
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
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4
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Wong NGK, Rankine CD, Anstöter CS, Dessent CEH. Photostability of the deprotonated forms of the UV filters homosalate and octyl salicylate: molecular dissociation versus electron detachment following UV excitation. Phys Chem Chem Phys 2022; 24:17068-17076. [PMID: 35791920 PMCID: PMC9301628 DOI: 10.1039/d2cp01612e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
While common molecular anions show a strong propensity to undergo electron detachment upon UV excitation, this process often occurs in competition with molecular ion dissociation. The factors that affect the balance between these two major possible decay pathways have not been well understood to date. Laser photodissociation spectroscopy of the deprotonated forms of the UV filter molecules, Homosalate (HS) and Octyl Salicylate (OS), i.e. [HS - H]- and [OS - H]-, was used to acquire gas-phase UV absorption spectra for [HS - H]- and [OS - H]-via photodepletion from 3.0-5.8 eV. No photofragmentation (i.e. dissociation of the ionic molecular framework) was observed for either [HS - H]- and [OS - H]- following photoexcitation, revealing that electron loss entirely dominates the electronic decay pathways for these systems. High-level quantum chemical calculations were used to map out the excited states associated with [HS - H]- and [OS - H]-, revealing that the minimum-energy crossing points (MECPs) between the S1 and S0 states are located in elevated regions of the potential energy surface, making internal conversion unlikely. These results are consistent with our experimental observation that electron detachment out-competes hot ground state molecular fragmentation. More generally, our results reveal that the competition between molecular dissociation and electron detachment following anion photoexcitation can be determined by the magnitude of the energy gap between the excitation energy and the MECPs, rather than being a simple function of whether the excitation energy lies above the anion's vertical detachment energy.
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Affiliation(s)
- Natalie G K Wong
- Department of Chemistry, University of York, Heslington, YO10 5DD, UK.
| | - Conor D Rankine
- Chemistry - School of Natural and Environmental Sciences, Newcastle University, Newcastle, upon Tyne, UK
| | - Cate S Anstöter
- Department of Chemistry, University of York, Heslington, YO10 5DD, UK.
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5
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Dobulis MA, McGee CJ, Sommerfeld T, Jarrold CC. Autodetachment over Broad Photon Energy Ranges in the Anion Photoelectron Spectra of [O 2- M] - ( M = Glyoxal, Methylglyoxal, or Biacetyl) Complex Anions. J Phys Chem A 2021; 125:9128-9142. [PMID: 34623818 DOI: 10.1021/acs.jpca.1c07163] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Complexes of anion-neutral pairs are prevalent in chemical and physical processes in the interstellar medium, the atmosphere, and biological systems, among others. However, bimolecular anionic species that cannot be described as simple ion-molecule complexes due to their competitive electron affinities have received less attention. In this study, the [O2-M]- (M = glyoxal, methylglyoxal, or biacetyl) anion photoelectron spectra obtained with several different photon energies are reported and interpreted in the context of ab initio calculations. The spectra do not resemble the photoelectron spectra of M- or O2- "solvated" by a neutral partner. Rather, all spectra are dominated by near-threshold autodetachment from what are likely transient dipole bound states of the cis conformers of the complex anions. Very low Franck-Condon overlap between the neutral M·O2 van der Waals clusters and the partial covalently bound complex anions results in low-intensity, broad direct detachment observed in the spectra. The [O2-glyoxal]- spectra measured with 2.88 and 3.495 eV photon energies additionally exhibit features at ∼0.5 eV electron kinetic energy, which is more difficult to explain, though there are numerous quasibound states of the anion that may be involved. Overall, these features point to the inadequacy of describing the complex anions as simple ion-molecule complexes.
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Affiliation(s)
- Marissa A Dobulis
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Conor J McGee
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Thomas Sommerfeld
- Department of Chemistry and Physics, Southeast Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
| | - Caroline Chick Jarrold
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
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6
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Lietard A, Verlet JRR, Slimak S, Jordan KD. Temporary Anion Resonances of Pyrene: A 2D Photoelectron Imaging and Computational Study. J Phys Chem A 2021; 125:7004-7013. [PMID: 34369146 DOI: 10.1021/acs.jpca.1c05586] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The low-energy electron-scattering resonances of pyrene were characterized using experimental and computational methods. Experimentally, a two-dimensional photoelectron imaging of the pyrene anion was used to probe the dynamics of resonances over the first 4 eV of the continuum. Computationally, the energies and character of the anion states were determined using equation-of-motion coupled cluster calculations, while taking specific care to avoid the collapse onto discretized continuum levels, and an application of the pairing theorem. Our results are in good agreement with the predictions of electron-scattering calculations that include an offset and with the pyrene anion absorption spectrum in a glass matrix. Taken together, we offer an assignment of the first five electronic resonances of pyrene. Some of the population in the lowest-energy 2B1u resonance was observed to decay to the ground electronic state of the anion, while all other resonances decay by a direct autodetachment. The astronomical relevance of a ground-state electron capture proceeding via a low-energy resonance in pyrene is discussed.
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Affiliation(s)
- Aude Lietard
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Stephen Slimak
- Department of Chemistry, University of Pittsburgh, Pittsburgh 15260, Pennsylvania, United States
| | - Kenneth D Jordan
- Department of Chemistry, University of Pittsburgh, Pittsburgh 15260, Pennsylvania, United States
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7
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Sagan CR, Garand E. Anion Resonances and Photoelectron Spectroscopy of the Tetracenyl Anion. J Phys Chem A 2021; 125:7014-7022. [PMID: 34370462 DOI: 10.1021/acs.jpca.1c05938] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The photoelectron spectroscopy of the tetracenyl anion using slow electron velocity-map imaging (SEVI) of cryogenically cooled ions is presented. The total photodetachment yield as a function of photon energy is used to reveal a rich manifold of anion excited states above the detachment threshold. The lowest energy anionic resonance has a sufficiently long lifetime to yield a vibrationally resolved absorption spectrum that can be directly compared with theoretical predictions. Excitation of this state mostly results in electron detachment via thermionic emission. The total photodetachment yield spectrum is used to select photon wavelengths that minimize the indirect detachment signal to allow acquisition of vibrationally resolved photoelectron spectra that can inform on the neutral tetracenyl radical. Assignment of spectral features corresponding to the ground and first excited state of the neutral 12-tetracenyl isomer is made with the aid of Franck-Condon simulations. This yields adiabatic electron affinity and term energies that differ significantly from the previously reported values. Weak features corresponding to the ground state of the minor 2-teracenyl and 1-tetracenyl isomers are also identified, which allows for the experimental determination of their electron affinities for the first time.
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Affiliation(s)
- Cole R Sagan
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Etienne Garand
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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8
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Gao XF, Xie JC, Li H, Meng X, Wu Y, Tian SX. Direct observation of long-lived cyanide anions in superexcited states. Commun Chem 2021; 4:13. [PMID: 36697555 PMCID: PMC9814559 DOI: 10.1038/s42004-021-00450-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 01/07/2021] [Indexed: 01/28/2023] Open
Abstract
The cyanide anion (CN-) has been identified in cometary coma, interstellar medium, planetary atmosphere and circumstellar envelopes, but its origin and abundance are still disputed. An isolated CN- is stabilized in the vibrational states up to ν = 17 of the electronic ground-state 1Σ+, but it is not thought to survive in the electronic or vibrational states above the electron autodetachment threshold, namely, in superexcited states. Here we report the direct observation of long-lived CN- yields of the dissociative electron attachment to cyanogen bromide (BrCN), and confirm that some of the CN- yields are distributed in the superexcited vibrational states ν ≥ 18 (1Σ+) or the superexcited electronic states 3Σ+ and 3Π. The triplet state can be accessed directly in the impulsive dissociation of BrCN- or by an intersystem transition from the superexcited vibrational states of CN-. The exceptional stability of CN- in the superexcited states profoundly influences its abundance and is potentially related to the production of other compounds in interstellar space.
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Affiliation(s)
- Xiao-Fei Gao
- Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemical Physics, University of Science and Technology of China, Hefei, China
| | - Jing-Chen Xie
- Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemical Physics, University of Science and Technology of China, Hefei, China
| | - Hao Li
- Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemical Physics, University of Science and Technology of China, Hefei, China
| | - Xin Meng
- Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemical Physics, University of Science and Technology of China, Hefei, China
| | - Yong Wu
- Institute of Applied Physics and Computational Mathematics, Beijing, China
| | - Shan Xi Tian
- Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemical Physics, University of Science and Technology of China, Hefei, China.
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9
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Ashworth EK, Anstöter CS, Verlet JRR, Bull JN. Autodetachment dynamics of 2-naphthoxide and implications for astrophysical anion abundance. Phys Chem Chem Phys 2021; 23:5817-5823. [PMID: 33686387 DOI: 10.1039/d1cp00261a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Astrochemical modelling has proposed that 10% or more of interstellar carbon could be tied up as polycyclic aromatic hydrocarbon (PAH) molecules. Developing reliable models of the interstellar carbon lifecycle requires calibration data obtained through laboratory studies on relevant chemical and physical processes, including on the photo-induced and electron-induced dynamics of potential interstellar PAHs. Here, the excited state dynamics of the S1(ππ*) state of 2-naphthoxide are investigated using frequency-, angle-, and time-resolved photoelectron imaging. Frequency-resolved photoelectron spectra taken over the S1(ππ*) band reveal low electron kinetic energy structure consistent with an indirect, vibrational mode-specific electron detachment mechanism. Time-resolved photoelectron imaging using a pump photon energy tuned to the 0-0 transition of the S1(ππ*) band (hν = 2.70 eV) and a non-resonant probe photon provides the excited state autodetachment lifetime at τ = 130 ± 10 fs. There is no evidence for internal conversion to the ground electronic state or a dipole-bound state. These results imply that 2-naphthoxide has no resilience to photodestruction through the absorption of visible radiation resonant with the S1(ππ*) band, and that electron capture by the S1(ππ*) state, which is formally a shape resonance, is not a doorway state to a stable interstellar anion.
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Affiliation(s)
- Eleanor K Ashworth
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, UK.
| | - Cate S Anstöter
- Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
| | - James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, UK.
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10
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Mensa-Bonsu G, Lietard A, Tozer DJ, Verlet JRR. Low energy electron impact resonances of anthracene probed by 2D photoelectron imaging of its radical anion. J Chem Phys 2020; 152:174303. [PMID: 32384861 DOI: 10.1063/5.0007470] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Electron-molecule resonances of anthracene were probed by 2D photoelectron imaging of the corresponding radical anion up to 3.7 eV in the continuum. A number of resonances were observed in both the photoelectron spectra and angular distributions, and most resonances showed clear autodetachment dynamics. The resonances were assigned using density functional theory calculations and are consistent with the available literature. Competition between direct and autodetachment, as well as signatures of internal conversion between resonances, was observed for some resonances. For the 12B2g resonance, a small fraction of population recovers the ground electronic state as evidenced by thermionic emission. Recovery of the ground electronic state offers a route of producing anions in an electron-molecule reaction; however, the energy at which this occurs suggests that anthracene anions cannot be formed in the interstellar medium by electron capture through this resonance.
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Affiliation(s)
- Golda Mensa-Bonsu
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Aude Lietard
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - David J Tozer
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, United Kingdom
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11
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Bull JN, Anstöter CS, Verlet JRR. Fingerprinting the Excited-State Dynamics in Methyl Ester and Methyl Ether Anions of Deprotonated para-Coumaric Acid. J Phys Chem A 2020; 124:2140-2151. [PMID: 32105474 DOI: 10.1021/acs.jpca.9b11993] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Chromophores based on the para-hydroxycinnamate moiety are widespread in the natural world, including as the photoswitching unit in photoactive yellow protein and as a sunscreen in the leaves of plants. Here, photodetachment action spectroscopy combined with frequency- and angle-resolved photoelectron imaging is used to fingerprint the excited-state dynamics over the first three bright action-absorption bands in the methyl ester anions (pCEs-) of deprotonated para-coumaric acid at a temperature of ∼300 K. The excited states associated with the action-absorption bands are classified as resonances because they are situated in the detachment continuum and are open to autodetachment. The frequency-resolved photoelectron spectrum for pCEs- indicates that all photon energies over the S1(ππ*) band lead to similar vibrational autodetachment dynamics. The S2(nπ*) band is Herzberg-Teller active and has comparable brightness to the higher lying 21(ππ*) band. The frequency-resolved photoelectron spectrum over the S2(nπ*) band indicates more efficient internal conversion to the S1(ππ*) state for photon energies resonant with the Franck-Condon modes (∼80%) compared with the Herzberg-Teller modes (∼60%). The third action-absorption band, which corresponds to excitation of the 21(ππ*) state, shows complex and photon energy-dependent dynamics, with 20-40% of photoexcited population internally converting to the S1(ππ*) state. There is also evidence for a mode-specific competition between prompt autodetachment and internal conversion on the red edge of the 21(ππ*) band. There is no evidence for recovery of the ground electronic state and statistical electron ejection (thermionic emission) following photoexcitation over any of the three action-absorption bands. The photoelectron spectra for the deprotonated methyl ether derivative (pCEt-) at photon energies over the S1(ππ*) and S2(nπ*) bands indicate diametrically opposed dynamics compared with pCEs-, namely, intense thermionic emission due to efficient recovery of the ground electronic state.
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Affiliation(s)
- James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Cate S Anstöter
- Department of Chemistry, Durham University, Durham DH1 3LE, U.K
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, U.K
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12
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Bull JN, Anstöter CS, Verlet JRR. Ultrafast valence to non-valence excited state dynamics in a common anionic chromophore. Nat Commun 2019; 10:5820. [PMID: 31862884 PMCID: PMC6925192 DOI: 10.1038/s41467-019-13819-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 11/27/2019] [Indexed: 12/19/2022] Open
Abstract
Non-valence states in neutral molecules (Rydberg states) have well-established roles and importance in photochemistry, however, considerably less is known about the role of non-valence states in photo-induced processes in anions. Here, femtosecond time-resolved photoelectron imaging is used to show that photoexcitation of the S1(ππ*) state of the methyl ester of deprotonated para-coumaric acid – a model chromophore for photoactive yellow protein (PYP) – leads to a bifurcation of the excited state wavepacket. One part remains on the S1(ππ*) state forming a twisted intermediate, whilst a second part leads to the formation of a non-valence (dipole-bound) state. Both populations eventually decay independently by vibrational autodetachment. Valence-to-non-valence internal conversion has hitherto not been observed in the intramolecular photophysics of an isolated anion, raising questions into how common such processes might be, given that many anionic chromophores have bright valence states near the detachment threshold. Photoactive biomolecules rely on chromophores whose photochemistry depends on the environment. Here, the excited state dynamics of a model for the anionic biochromophore in photoactive yellow protein is investigated by time-resolved photoelectron spectroscopy showing involvement of a non-valence state, and lack of E-Z isomerisation in the gas phase.
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Affiliation(s)
- James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich, NR4 7TJ, UK
| | - Cate S Anstöter
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK
| | - Jan R R Verlet
- Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK.
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13
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Bull JN, Scholz MS, Carrascosa E, Kristiansson MK, Eklund G, Punnakayathil N, de Ruette N, Zettergren H, Schmidt HT, Cederquist H, Stockett MH. Ultraslow radiative cooling of Cn− (n = 3–5). J Chem Phys 2019; 151:114304. [DOI: 10.1063/1.5114678] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- James N. Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - Michael S. Scholz
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
| | - Eduardo Carrascosa
- Laboratoire de Chimie Physique Moléculaire, École Polytechnique Fédérale de Lausanne, EPFL SB ISIC LCPM, Station 6, CH-1015 Lausanne, Switzerland
| | | | - Gustav Eklund
- Department of Physics, Stockholm University, SE-10691 Stockholm, Sweden
| | | | | | | | | | - Henrik Cederquist
- Department of Physics, Stockholm University, SE-10691 Stockholm, Sweden
| | - Mark H. Stockett
- Department of Physics, Stockholm University, SE-10691 Stockholm, Sweden
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14
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Bull JN, West CW, Anstöter CS, da Silva G, Bieske EJ, Verlet JRR. Ultrafast photoisomerisation of an isolated retinoid. Phys Chem Chem Phys 2019; 21:10567-10579. [PMID: 31073587 DOI: 10.1039/c9cp01624d] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The photoinduced excited state dynamics of gas-phase trans-retinoate (deprotonated trans-retinoic acid, trans-RA-) are studied using tandem ion mobility spectrometry coupled with laser spectroscopy, and frequency-, angle- and time-resolved photoelectron imaging. Photoexcitation of the bright S3(ππ*) ← S0 transition leads to internal conversion to the S1(ππ*) state on a ≈80 fs timescale followed by recovery of S0 and concomitant isomerisation to give the 13-cis (major) and 9-cis (minor) photoisomers on a ≈180 fs timescale. The sub-200 fs stereoselective photoisomerisation parallels that for the retinal protonated Schiff base chromophore in bacteriorhodopsin. Measurements on trans-RA- in methanol using the solution photoisomerisation action spectroscopy technique show that 13-cis-RA- is also the principal photoisomer, although the 13-cis and 9-cis photoisomers are formed with an inverted branching ratio with photon energy in methanol when compared with the gas phase, presumably due to solvent-induced modification of potential energy surfaces and inhibition of electron detachment processes. Comparison of the gas-phase time-resolved data with transient absorption spectroscopy measurements on retinoic acid in methanol suggest that photoisomerisation is roughly six times slower in solution. This work provides clear evidence that solvation significantly affects the photoisomerisation dynamics of retinoid molecules.
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Affiliation(s)
- James N Bull
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, UK.
| | - Christopher W West
- Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - Cate S Anstöter
- Department of Chemistry, Durham University, Durham DH1 3LE, UK
| | - Gabriel da Silva
- Department of Chemical Engineering, University of Melbourne, Parkville, VIC 3010, Australia
| | - Evan J Bieske
- School of Chemistry, University of Melbourne, Parkville, VIC 3010, Australia
| | - Jan R R Verlet
- Department of Chemistry, Durham University, Durham DH1 3LE, UK
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15
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Parkes MA, Bennett A, Fielding HH. A photoelectron imaging and quantum chemistry study of the deprotonated cyan fluorescent protein chromophore anion. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1603410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
| | - Anabel Bennett
- Department of Chemistry, University College London, London, UK
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16
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Khatymov RV, Muftakhov MV, Tuktarov RF, Raitman OA, Shokurov AV, Pankratyev EY. Fragmentation and slow autoneutralization of isolated negative molecular ions of phthalocyanine and tetraphenylporphyrin. J Chem Phys 2019; 150:134301. [PMID: 30954040 DOI: 10.1063/1.5087182] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Macrocyclic tetrapyrrolic compounds, such as naturally occurring or artificial porphyrins and phthalocyanines, have unique and highly attractive properties for applications in medicine and technology. The interaction of free-base phthalocyanine (H2Pc) and tetraphenylporphyrin (H2TPP) molecules with low-energy (0-15 eV) electrons was studied in vacuo by means of negative ion resonant electron capture mass spectrometry. Close similarities in formation and decay of negative ions of these compounds were revealed. Efficient formation of long-lived molecular negative ions (MNIs) was observed in the incident electron energy range of 0-8 eV, unprecedentedly wide for organic compounds and comparable to the range characteristic to carbon atomic clusters, fullerenes. Experiments testify to the strong persistence of MNIs of both compounds to dissociative decay, isomerization, and electron autodetachment. Lifetimes of MNIs as a function of incident electron energy were measured and it was concluded that the isolated anions may retain additional electrons in a time scale of up to hundreds of seconds at standard temperature due to the high adiabatic electron affinity of these large molecules. For the representatives of dyes and photochromic compounds comprehensively studied in terms of interaction with light, the present work highlights yet another unique property of these molecules, namely the capability to attach and durably retain an additional electron of low, pre-ionization energy.
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Affiliation(s)
- Rustem V Khatymov
- Institute of Molecule and Crystal Physics-Subdivision of the Ufa Federal Research Centre of the Russian Academy of Sciences (IMCP UFRC RAS), Prospekt Oktyabrya 151, Ufa 450075, Russia
| | - Mars V Muftakhov
- Institute of Molecule and Crystal Physics-Subdivision of the Ufa Federal Research Centre of the Russian Academy of Sciences (IMCP UFRC RAS), Prospekt Oktyabrya 151, Ufa 450075, Russia
| | - Renat F Tuktarov
- Institute of Molecule and Crystal Physics-Subdivision of the Ufa Federal Research Centre of the Russian Academy of Sciences (IMCP UFRC RAS), Prospekt Oktyabrya 151, Ufa 450075, Russia
| | - Oleg A Raitman
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences (IPCE RAS), Leninsky prospect, 31k4, Moscow 199071, Russia
| | - Alexander V Shokurov
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences (IPCE RAS), Leninsky prospect, 31k4, Moscow 199071, Russia
| | - Evgeniy Yu Pankratyev
- Institute of Molecule and Crystal Physics-Subdivision of the Ufa Federal Research Centre of the Russian Academy of Sciences (IMCP UFRC RAS), Prospekt Oktyabrya 151, Ufa 450075, Russia
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17
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Yuan Q, Kong XT, Hou GL, Jiang L, Wang XB. Electrospray ionization photoelectron spectroscopy of cryogenic [EDTA·M(ii)]2− complexes (M = Ca, V–Zn): electronic structures and intrinsic redox properties. Faraday Discuss 2019; 217:383-395. [DOI: 10.1039/c8fd00175h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A systematic photoelectron spectroscopy and theoretical study of divalent transition metal EDTA complexes illustrating the intrinsic correlations of redox properties in the gas and solution phases.
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Affiliation(s)
- Qinqin Yuan
- Physical Sciences Division
- Pacific Northwest National Laboratory
- Richland
- USA
- State Key Laboratory of Molecular Reaction Dynamics
| | - Xiang-Tao Kong
- State Key Laboratory of Molecular Reaction Dynamics
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
- Dalian 116023
- China
| | - Gao-Lei Hou
- Physical Sciences Division
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Ling Jiang
- State Key Laboratory of Molecular Reaction Dynamics
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
- Dalian 116023
- China
| | - Xue-Bin Wang
- Physical Sciences Division
- Pacific Northwest National Laboratory
- Richland
- USA
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18
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Kregel SJ, Thurston GK, Garand E. Photoelectron spectroscopy of anthracene and fluoranthene radical anions. J Chem Phys 2018; 148:234306. [PMID: 29935502 DOI: 10.1063/1.5036757] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report the slow electron velocity map imaging spectroscopy of cryogenically cooled anthracene and fluoranthene radical anions, two similarly sized polycyclic aromatic hydrocarbon molecules. The results allow us to examine the lowest energy singlet and triplet states in the neutral molecules on equal footing from the anionic ground state. The analysis of the experimental spectra is aided by harmonic calculations and Franck-Condon simulations, which generally show good agreement with experimental values and spectra. The electron affinity of fluoranthene is measured to be 0.757(2) eV, which is larger than that of anthracene at 0.532(3) eV. The lowest energy triplet state in anthracene is observed at 1.872(3) eV above the singlet ground state, while that of fluoranthene is observed at 2.321(2) eV above its singlet ground state. Comparisons of experimental and calculated spectra show that in addition to the Franck-Condon active modes, there is a clear presence of vibrational modes that gain intensity via vibronic coupling in both the singlet and triplet states in both molecules. In addition, the triplet state generally exhibits increased vibronic coupling compared to the singlet state, with the fluoranthene triplet state exhibiting evidence of distortion from C2v symmetry.
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Affiliation(s)
- Steven J Kregel
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, USA
| | - Glen K Thurston
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, USA
| | - Etienne Garand
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave., Madison, Wisconsin 53706, USA
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19
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Khatymov RV, Muftakhov MV, Shchukin PV. Negative ions, molecular electron affinity and orbital structure of cata-condensed polycyclic aromatic hydrocarbons. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2017; 31:1729-1741. [PMID: 28753734 DOI: 10.1002/rcm.7945] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 07/13/2017] [Accepted: 07/21/2017] [Indexed: 06/07/2023]
Abstract
RATIONALE Polycyclic aromatic hydrocarbons are molecules of ecological, astrochemical significance that find practical applications in organic electronics, photonics and the chemical synthesis of novel materials. The utility of these molecules often implies the occurrence of their ionized forms. Studies in the gas phase of elementary processes of energy-controlled interaction of molecules with low-energy electrons shed light on the mechanisms of transient negative ion formation and evolution. METHODS Experiments with the individual compounds representing homologous and/or isomeric series of cata-condensed polyaromatic hydrocarbons were carried out by means of negative ion mass spectrometry in the resonant electron capture mode. Literature data obtained by complementary techniques and theoretical quantum chemical methods (ab initio and density functional theory (DFT)) were invoked to treat the experimental observations. RESULTS Most polycyclic aromatic hydrocarbon (PAH) molecules form long-lived molecular negative ions when exposed to free electrons of thermal or epi-thermal energy, and no fragmentation is observed up to ca 5 eV. The lifetimes of such ions with respect to the spontaneous loss of extra-electron vary from tens of microseconds for angular and branched PAH molecules to milliseconds for linear ones, and correlate with the adiabatic electron affinity (EA) of molecules. Detailed analysis of the electronic (orbital) structure of the molecules made it possible to rationalize the relatively low EAs of angular and branched PAH compared with those of linear ones. CONCLUSIONS The obtained results contribute to the field of electron-molecule interactions and may be of importance for the better comprehension of the functioning of organic electronics, for the synthesis of relevant novel materials, and the development of efficient analytical methods capable of discriminating structural isomers.
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Affiliation(s)
- Rustem V Khatymov
- Institute of Molecule and Crystal Physics, Ufa Research Center of Russian Academy of Sciences, IМСР URC RAS, Prospekt Oktyabrya 151, Ufa, 450075, Russia
| | - Mars V Muftakhov
- Institute of Molecule and Crystal Physics, Ufa Research Center of Russian Academy of Sciences, IМСР URC RAS, Prospekt Oktyabrya 151, Ufa, 450075, Russia
| | - Pavel V Shchukin
- Institute of Molecule and Crystal Physics, Ufa Research Center of Russian Academy of Sciences, IМСР URC RAS, Prospekt Oktyabrya 151, Ufa, 450075, Russia
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20
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Stanley LH, Anstöter CS, Verlet JRR. Resonances of the anthracenyl anion probed by frequency-resolved photoelectron imaging of collision-induced dissociated anthracene carboxylic acid. Chem Sci 2017; 8:3054-3061. [PMID: 28451374 PMCID: PMC5380881 DOI: 10.1039/c6sc05405f] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 02/01/2017] [Indexed: 01/04/2023] Open
Abstract
The use of CID and photoelectron spectroscopy of organic carboxylic acid anions is discussed as a route to studying the dynamics of resonances in polyaromatic hydrocarbon (PAH) anions.
Resonances in polyaromatic hydrocarbon (PAH) anions are key intermediates in a number of processes such as electron transfer in organic electronics and electron attachment in the interstellar medium. Here we present a frequency- and angle-resolved photoelectron imaging study of the 9-anthracenyl anion generated through collision induced dissociation (CID) of its electrosprayed deprotonated anthracene carboxylic acid anion. We show that a number of π* resonances are active in the first 2.5 eV above the threshold. The photoelectron spectra and angular distributions revealed that nuclear dynamics compete with autodetachment for one of the resonances, while higher-lying resonances were dominated by prompt autodetachment. Based on electronic structure calculations, these observations were accounted for on the basis of the expected autodetachment rates of the resonances. Virtually no ground state recovery was observed, suggesting that the smallest deprotonated PAH that leads to ground state recovery is the tetracenyl anion, for which clear thermionic emission has been observed. The use of CID and photodissociation of organic carboxylic acid anions is discussed as a route to studying the dynamics of resonances in larger PAH anions.
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Affiliation(s)
| | - Cate S Anstöter
- Department of Chemistry , Durham University , Durham DH1 3LE , UK .
| | - Jan R R Verlet
- Department of Chemistry , Durham University , Durham DH1 3LE , UK .
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21
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Bull JN, Verlet JRR. Dynamics of π*-resonances in anionic clusters of para-toluquinone. Phys Chem Chem Phys 2017; 19:26589-26595. [DOI: 10.1039/c7cp03628k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Frequency-resolved photoelectron spectroscopy applied to mass-selected cluster anions is an insightful approach to characterise the dynamics of π*-resonances with microsolvation.
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Affiliation(s)
- James N. Bull
- Department of Chemistry
- Durham University
- Durham DH1 3LE
- UK
- School of Chemistry
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22
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West CW, Bull JN, Verlet JRR. Charged Particle Imaging of the Deprotonated Octatrienoic Acid Anion: Evidence for a Photoinduced Cyclization Reaction. J Phys Chem Lett 2016; 7:4635-4640. [PMID: 27809535 DOI: 10.1021/acs.jpclett.6b02302] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9-CO2]-, shows the formation of [C7H9]- and loss of H- at hν = 4.13 eV. Using velocity map imaging, the H- fragment was characterized to have a Boltzmann-like kinetic energy distribution consistent with dissociation on a ground electronic state. Similar dynamics were not observed at hν = 4.66 eV even though there is clear evidence for recovery of the ground electronic state of [C7H9-CO2]-. In accord with supporting electronic structure calculations, the production of H- at hν = 4.13 eV is explained by excited-state dissociation of CO2 to form [C7H9]-, which subsequently undergoes a ring-closure isomerization reaction to yield toluene and H-. These data represent the first evidence for a photoinduced ring-closing isomerization reaction in an anionic polyene and provides an interesting example of the rich anion dynamics that can occur in the detachment continuum and that can influence photochemistry.
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Affiliation(s)
- Christopher W West
- Department of Chemistry, Graduate School of Science, Kyoto University , Kitashirakawa Oiwake-cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - James N Bull
- School of Chemistry, University of Melbourne , Parkville, Melbourne, Victoria 3010, Australia
| | - Jan R R Verlet
- Department of Chemistry, University of Durham , Durham DH1 3LE, United Kingdom
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23
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Anstöter CS, Bull JN, Verlet JR. Ultrafast dynamics of temporary anions probed through the prism of photodetachment. INT REV PHYS CHEM 2016. [DOI: 10.1080/0144235x.2016.1203522] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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24
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Bull JN, West CW, Verlet JRR. Ultrafast dynamics of formation and autodetachment of a dipole-bound state in an open-shell π-stacked dimer anion. Chem Sci 2016; 7:5352-5361. [PMID: 30155188 PMCID: PMC6020752 DOI: 10.1039/c6sc01062h] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 04/23/2016] [Indexed: 12/15/2022] Open
Abstract
Isolated π-stacked dimer radical anions present the simplest model of an excess electron in a π-stacked environment. Here, frequency-, angle-, and time-resolved photoelectron imaging together with electronic structure calculations have been used to characterise the π-stacked coenzyme Q0 dimer radical anion and its exited state dynamics. In the ground electronic state, the excess electron is localised on one monomer with a planar para-quinone ring, which is solvated by the second monomer in which carbonyl groups are bent out of the para-quinone ring plane. Through the π-stacking interaction, the dimer anion exhibits a number of charge-transfer (intermolecular) valence-localised resonances situated in the detachment continuum that undergo efficient internal conversion to a cluster dipole-bound state (DBS) on a ∼60 fs timescale. In turn, the DBS undergoes vibration-mediated autodetachment on a 2.0 ± 0.2 ps timescale. Experimental vibrational structure and supporting calculations assign the intermolecular dynamics to be facilitated by vibrational wagging modes of the carbonyl groups on the non-planar monomer. At photon energies ∼0.6-1.0 eV above the detachment threshold, a competition between photoexcitation of an intermolecular resonance leading to the DBS, and photoexcitation of an intramolecular resonance leading to monomer-like dynamics further illustrates the π-stacking specific dynamics. Overall, this study provides the first direct observation of both internal conversion of resonances into a DBS, and characterisation of a vibration-mediated autodetachment in real-time.
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Affiliation(s)
- James N Bull
- Department of Chemistry , Durham University , South Road , Durham DH1 3LE , UK .
| | - Christopher W West
- Department of Chemistry , Durham University , South Road , Durham DH1 3LE , UK .
| | - Jan R R Verlet
- Department of Chemistry , Durham University , South Road , Durham DH1 3LE , UK .
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