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Diprose JA, Richardson V, Regan P, Roberts A, Burdin S, Tsikritea A, Mavrokoridis K, Heazlewood BR. Spatial and Temporal Detection of Ions Ejected from Coulomb Crystals. J Phys Chem A 2024; 128:3900-3909. [PMID: 38588488 PMCID: PMC11103685 DOI: 10.1021/acs.jpca.3c08132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/14/2024] [Accepted: 03/15/2024] [Indexed: 04/10/2024]
Abstract
Coulomb crystals have proven to be powerful and versatile tools for the study of ion-molecule reactions under cold and controlled conditions. Reactions in Coulomb crystals are typically monitored through a combination of in situ fluorescence imaging of the laser-cooled ions and destructive time-of-flight mass spectrometry measurements of the ejected ions. However, neither of these techniques is able to provide direct structural information on the positions of nonfluorescing "dark" ions within the crystal. In this work, structural information is obtained using a phosphor screen and a microchannel plate detector in conjunction with a Timepix3 camera. The Timepix3 camera simultaneously records the spatial and temporal distribution of all ions that strike the phosphor screen detector following crystal ejection at a selected reaction time. A direct comparison can be made between the observed Timepix3 ion distributions and the distributions established from SIMION simulations of the ion trajectories through the apparatus and onto the detector. Quantitative agreement is found between the measured Timepix3 signal and the properties of Coulomb crystals assigned using fluorescence imaging─independently confirming that the positions and numbers of nonfluorescing ions within Coulomb crystals can be accurately determined using molecular dynamics simulations. It is anticipated that the combination of high-resolution spatial and temporal data will facilitate new measurements of the ion properties within Coulomb crystals.
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Affiliation(s)
- Jake A. Diprose
- Department
of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.
| | | | - Paul Regan
- Department
of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.
| | - Adam Roberts
- Department
of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.
| | - Sergey Burdin
- Department
of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.
| | - Andriana Tsikritea
- Department
of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.
- Department
of Physics, TU Dortmund, Dortmund 44227, Germany
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Heathcote D, Robertson PA, Butler AA, Ridley C, Lomas J, Buffett MM, Bell M, Vallance C. Electron-induced dissociation dynamics studied using covariance-map imaging. Faraday Discuss 2022; 238:682-699. [PMID: 35781475 DOI: 10.1039/d2fd00033d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Recently, covariance analysis has found significant use in the field of chemical reaction dynamics. When coupled with data from product time-of-flight mass spectrometry and/or multi-mass velocity-map imaging, it allows us to uncover correlations between two or more ions formed from the same parent molecule. While the approach has parallels with coincidence measurements, covariance analysis allows experiments to be performed at much higher count rates than traditional coincidence methods. We report results from electron-molecule crossed-beam experiments, in which covariance analysis is used to elucidate the dissociation dynamics of multiply-charged ions formed by electron ionisation over the energy range from 50 to 300 eV. The approach is able to isolate signal contributions from multiply charged ions even against a very large 'background' of signal arising from dissociation of singly-charged parent ions. Covariance between the product time-of-flight spectra identifies pairs of fragments arising from the same parent ions, while covariances between the velocity-map images ('recoil-frame covariances') reveal the relative velocity distributions of the ion pairs. We show that recoil-frame covariance analysis can be used to distinguish between multiple plausible dissociation mechanisms, including multi-step processes, and that the approach becomes particularly powerful when investigating the fragmentation dynamics of larger molecules with a higher number of possible fragmentation pathways.
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Affiliation(s)
- David Heathcote
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Patrick A Robertson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Alexander A Butler
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Cian Ridley
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - James Lomas
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Madeline M Buffett
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Megan Bell
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, UK.
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Robertson PA, Heathcote D, Milešević D, Vallance C. Imaging the Dynamics of the Electron Ionization of C 2F 6. J Phys Chem A 2022; 126:7221-7229. [PMID: 36194389 PMCID: PMC9574930 DOI: 10.1021/acs.jpca.2c05606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The dissociation of C2F6 following
electron
ionization at 100 eV has been studied using multimass velocity-map
ion imaging and covariance-map imaging analysis. Single ionization
events form parent C2F6+ cations
in an ensemble of electronic states, which follow a multiplex of relaxation
pathways to eventually dissociate into ionic and neutral fragment
products. We observe CF3+, CF2+, CF+, C+, F+, C2F5+, C2F4+, C2F2+, and C2F+ ions, all of which can reasonably be formed from singly charged
parent ions. Dissociation along the C–C bond typically forms
slow-moving, internally excited products, whereas C–F bond
cleavage is rapid and impulsive. Dissociation from the à state
of the cation preferentially forms C2F5+ and neutral F along a purely repulsive surface. No other
electronic state of the ion will form this product pair at the electron
energies studied in this work, nor do we observe any crossing onto
this surface from higher-lying states of the parent ion. Multiply
charged dissociative pathways are also explored, and we note characteristic
high kinetic energy release channels due to Coulombic repulsion between
charged fragments. The most abundant ion pair we observe is (CF2+, CF+), and we also observe ion pair
signals in the covariance maps associated with almost all possible
C–C bond cleavage products as well as between F+ and each of CF3+, CF2+, CF+, and C+. No covariance between F+ and C2F5+ is observed, implying
that any C2F5+ formed with F+ is unstable and undergoes secondary fragmentation. Dissociation
of multiply charged parent ions occurs via a number of mechanisms,
details of which are revealed by recoil-frame covariance-map imaging.
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Affiliation(s)
| | - David Heathcote
- Chemistry Research Laboratory, University of Oxford, OxfordOX1 3TA, U.K
| | - Dennis Milešević
- Chemistry Research Laboratory, University of Oxford, OxfordOX1 3TA, U.K
| | - Claire Vallance
- Chemistry Research Laboratory, University of Oxford, OxfordOX1 3TA, U.K
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Crane SW, Lee JWL, Ashfold MNR. Multi-mass velocity map imaging study of the 805 nm strong field ionization of CF 3I. Phys Chem Chem Phys 2022; 24:18830-18840. [PMID: 35904364 DOI: 10.1039/d2cp02449g] [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
Multi-mass velocity map imaging studies of charged fragments formed by near infrared strong field ionization together with covariance map image analysis offer a new window through which to explore the dissociation dynamics of several different highly charged parent cations, simultaneously - as demonstrated here for the case of CF3IZ+ cations with charges Z ranging from 1 to at least 5. Previous reports that dissociative ionization of CF3I+ cations yields CF3+, I+ and CF2I+ fragment ions are confirmed, and some of the CF3+ fragments are deduced to undergo secondary loss of one or more neutral F atoms. Covariance map imaging confirms the dominance of CF3+ + I+ products in the photodissociation of CF3I2+ cations and, again, that some of the primary CF3+ photofragments can shed one or more F atoms. Rival charge symmetric dissociation pathways to CF2I+ + F+ and to IF+ + CF2+ products and charge asymmetric dissociations to CF3 + I2+ and CF2I2+ + F products are all also identified. The findings for parent cations with Z ≥ 3 are wholly new. In all cases, the fragment recoil velocity distributions imply dissociation dynamics in which coulombic repulsive forces play a dominant role. The major photoproducts following dissociation of CF3I3+ ions are CF3+ and I2+, with lesser contributions from the rival CF2I2+ + F+ and CF32+ + I+ channels. The CF32+ fragment ion images measured at higher incident intensities show a faster velocity sub-group consistent with their formation in tandem with I2+ fragments, from photodissociation of CF3I4+ parent ions. The measured velocity distributions of the I3+ fragment ions contain features attributable to CF3I5+ photodissociation to CF32+ + I3+ and the images of fragments with mass to charge (m/z) ratio ∼31 show formation of I4+ products that must originate from parent ions with yet higher Z.
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Affiliation(s)
- Stuart W Crane
- School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK.
| | - Jason W L Lee
- Department of Chemistry, University of Oxford, Oxford, OX1 3TA, UK.,Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany
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Heathcote D, Vallance C. Partial and Contingent Recoil-Frame Covariance-Map Imaging. J Phys Chem A 2021; 125:7092-7098. [PMID: 34351156 DOI: 10.1021/acs.jpca.1c04548] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
When applied to multimass velocity-map imaging data, covariance analysis reveals correlations between different fragment ions formed from the same parent molecule and can provide detailed insights into the fragmentation dynamics. Covariances between the time-of-flight signals for two different ions show that they are formed in the same event, while covariances between their velocity-map images, often referred to as "recoil-frame covariances", reveal details of the correlated motion of the two fragments. In many cases, covariance analysis is complicated by the fact that fluctuations in experimental parameters such as laser or molecular beam intensities can lead to apparent correlations between unrelated ions. In the context of time-of-flight covariance signals, this problem has been overcome by the introduction of partial covariance and contingent covariance approaches. Here, we apply these approaches to recoil-frame covariance-map images. We also demonstrate that in many cases the total signal within each experimental cycle can be used as a useful proxy for independent explicit measurements of the varying experimental parameter(s).
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Affiliation(s)
- David Heathcote
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
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Vallance C, Heathcote D, Lee JWL. Covariance-Map Imaging: A Powerful Tool for Chemical Dynamics Studies. J Phys Chem A 2021; 125:1117-1133. [DOI: 10.1021/acs.jpca.0c10038] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K
| | - David Heathcote
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K
| | - Jason W. L. Lee
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford OX1 3TA, U.K
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Köckert H, Heathcote D, Lee JWL, Vallance C. Covariance-map imaging study into the fragmentation dynamics of multiply charged CF3I formed in electron-molecule collisions. Mol Phys 2020. [DOI: 10.1080/00268976.2020.1811909] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Hansjochen Köckert
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford, UK
| | - David Heathcote
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford, UK
| | - Jason W. L. Lee
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford, UK
| | - Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford, UK
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Gregory J, Verlet JRR, Bull JN. Spectroscopic characterisation of radical polyinterhalogen molecules. Phys Chem Chem Phys 2020; 22:8284-8288. [PMID: 32270847 DOI: 10.1039/d0cp01311k] [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
Spectroscopic characterisations of the radical polyinterhalogen molecules IF2 and I2F are reported using anion photoelectron spectroscopy. The corresponding parent anions, IF2- and I2F-, are common products formed in hard Ar-CF3I plasmas and are relevant in the semiconductor manufacture industry. The I2F- species, which is present as the [I-I-F]- isomer, is a "non-classical" polyinterhalogen.
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Affiliation(s)
- Joe Gregory
- School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, UK.
| | - Jan R R Verlet
- Department of Chemistry, Durham University, South Road, 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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Vallance C. Multi-mass velocity-map imaging studies of photoinduced and electron-induced chemistry. Chem Commun (Camb) 2019; 55:6336-6352. [PMID: 31099379 DOI: 10.1039/c9cc02426c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Multi-mass velocity-map imaging (VMI) is becoming established as a promising method for probing the dynamics of a variety of gas-phase chemical processes. We provide an overview of velocity-map imaging and multi-mass velocity-map imaging techniques, highlighting examples in which these approaches have been used to provide mechanistic insights into a range of photoinduced and electron-induced chemical processes. Multi-mass detection capabilities have also led to the development of two new tools for the chemical dynamics toolbox, in the form of Coulomb-explosion imaging and covariance-map imaging. These allow details of molecular structure to be followed in real time over the course of a chemical reaction, offering the tantalising prospect of recording real-time 'molecular movies' of chemical dynamics. As these new methods become established within the reaction dynamics community, they promise new mechanistic insights into chemistry relevant to fields ranging from atmospheric chemistry and astrochemistry through to synthetic organic photochemistry and biology.
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Affiliation(s)
- Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd, Oxford OX1 3TA, UK.
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