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Sparling C, Ruget A, Ireland L, Kotsina N, Ghafur O, Leach J, Townsend D. The importance of molecular axis alignment and symmetry-breaking in photoelectron elliptical dichroism. J Chem Phys 2023; 159:214301. [PMID: 38038198 DOI: 10.1063/5.0180361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 11/06/2023] [Indexed: 12/02/2023] Open
Abstract
Photoelectron angular distributions (PADs) produced from the photoionization of chiral molecules using elliptically polarized light exhibit a forward/backward asymmetry with respect to the optical propagation direction. By recording these distributions using the velocity-map imaging (VMI) technique, the resulting photoelectron elliptical dichroism (PEELD) has previously been demonstrated as a promising spectroscopic tool for studying chiral molecules in the gas phase. The use of elliptically polarized laser pulses, however, produces PADs (and consequently, PEELD distributions) that do not exhibit cylindrical symmetry about the propagation axis. This leads to significant limitations and challenges when employing conventional VMI acquisition and data processing strategies. Using novel photoelectron image analysis methods based around Hankel transform reconstruction tomography and machine learning, however, we have quantified-for the first time-significant symmetry-breaking contributions to PEELD signals that are of a comparable magnitude to the symmetric terms in the multiphoton ionization of (1R,4R)-(+)- and (1S,4S)-(-)-camphor. This contradicts any assumptions that symmetry-breaking can be ignored when reconstructing VMI data. Furthermore, these same symmetry-breaking terms are expected to appear in any experiment where circular and linear laser fields are used together. This ionization scheme is particularly relevant for investigating dynamics in chiral molecules, but it is not limited to them. Developing a full understanding of these terms and the role they play in the photoionization of chiral molecules is of clear importance if the potential of PEELD and related effects for future practical applications is to be fully realized.
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Affiliation(s)
- Chris Sparling
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Alice Ruget
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Lewis Ireland
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Nikoleta Kotsina
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Omair Ghafur
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Jonathan Leach
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Dave Townsend
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
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Milešević D, Popat D, Gellersen P, Liu Z, Stimson J, Robertson P, Green A, Vallance C. Design and characterization of an optical-fiber-coupled laser-induced desorption source for gas-phase dynamics experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:114105. [PMID: 37987631 DOI: 10.1063/5.0170080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 11/03/2023] [Indexed: 11/22/2023]
Abstract
Preparation of neutral non-volatile molecules intact in the gas phase for mass spectrometry or chemical dynamics experiments remains a challenge for many classes of molecules. Here, we report the design and characterization of a fiber-coupled laser-based thermal desorption source capable of preparing intact neutral molecules at high molecular densities in the gas phase for use in velocity-map imaging experiments. Within this source, the sample is deposited onto a thin tantalum foil. Irradiation of the foil from the reverse side by a focused laser beam leads to highly localized heating of the sample, resulting in desorption of a plume of molecules into the gas phase. The fiber-coupled design simplifies the alignment of the desorption laser beam, and the ability to rotate the foil relative to the fixed laser beam allows the sample to be continually refreshed under vacuum. We use 118 nm photoionization of three test molecules-uracil, adenine, and phenylalanine-to characterize the source and to demonstrate various aspects of its performance. These include the dependence of the velocity-map imaging performance on the size of the interaction region and the dependence of the laser-induced desorption source emission on desorption laser power and heating time. Signal levels recorded in these measurements are comparable to those we typically obtain in similar experiments using a pulsed supersonic molecular beam, and we, therefore, believe that the source has considerable potential for use in a wide range of chemical dynamics and other experiments.
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Affiliation(s)
- Dennis Milešević
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Divya Popat
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Paul Gellersen
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Zhihao Liu
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Joseph Stimson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Patrick Robertson
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Andrew Green
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
| | - Claire Vallance
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Rd., Oxford OX1 3TA, United Kingdom
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Sparling C, Crane SW, Ireland L, Anderson R, Ghafur O, Greenwood JB, Townsend D. Velocity-map imaging of photoelectron circular dichroism in non-volatile molecules using a laser-based desorption source. Phys Chem Chem Phys 2023; 25:6009-6015. [PMID: 36752555 DOI: 10.1039/d2cp05880d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
We present an initial demonstration of a velocity-map imaging (VMI) experiment using a back-irradiation laser-based desorption source directly integrated into the electrode assembly. This has the potential to greatly expand the utility of the popular VMI approach by permitting its use with high density plumes of non-volatile molecular samples. Photoelectron circular dichroism measurements on the phenylalanine molecule using 400 nm multiphoton ionization are used to illustrate this novel method, revealing forward-backward emission asymmetries on the order of 7%.
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Affiliation(s)
- Chris Sparling
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Stuart W Crane
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Lewis Ireland
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Ross Anderson
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Omair Ghafur
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
| | - Jason B Greenwood
- School of Mathematics and Physics, Queen's University Belfast, Belfast, BT7 1NN, UK
| | - Dave Townsend
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. .,Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK
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Bocková J, Rebelo A, Ryszka M, Pandey R, Mészáros D, Limão-Vieira P, Papp P, Mason NJ, Townsend D, Nixon KL, Vizcaino V, Poully JC, Eden S. Thermal desorption effects on fragment ion production from multi-photon ionized uridine and selected analogues. RSC Adv 2021; 11:20612-20621. [PMID: 35479354 PMCID: PMC9033967 DOI: 10.1039/d1ra01873f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Accepted: 05/09/2021] [Indexed: 12/22/2022] Open
Abstract
Experiments on neutral gas-phase nucleosides are often complicated by thermal lability. Previous mass spectrometry studies of nucleosides have identified enhanced relative production of nucleobase ions (e.g. uracil+ from uridine) as a function of desorption temperature to be the critical indicator of thermal decomposition. On this basis, the present multi-photon ionization (MPI) experiments demonstrate that laser-based thermal desorption is effective for producing uridine, 5-methyluridine, and 2′-deoxyuridine targets without thermal decomposition. Our experiments also revealed one notable thermal dependence: the relative production of the sugar ion C5H9O4+ from intact uridine increased substantially with the desorption laser power and this only occurred at MPI wavelengths below 250 nm (full range studied 222–265 nm). We argue that this effect can only be rationalized plausibly in terms of changing populations of different isomers, tautomers, or conformers in the target as a function of the thermal desorption conditions. Furthermore, the wavelength threshold behavior of this thermally-sensitive MPI channel indicates a critical dependence on neutral excited state dynamics between the absorption of the first and second photons. The experimental results are complemented by density functional theory (DFT) optimizations of the lowest-energy structure of uridine and two further conformers distinguished by different orientations of the hydroxymethyl group on the sugar part of the molecule. The energies of the transitions states between these three conformers are low compared with the energy required for decomposition. This work reveals the first experimental evidence supporting isomer-dependence in the radiation response of a nucleoside.![]()
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Affiliation(s)
- J Bocková
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK
| | - A Rebelo
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK .,Atomic and Molecular Collisions Laboratory, CEFITEC, Department of Physics, FCT - Universidade NOVA de Lisboa P-2829-516 Caparica Portugal
| | - M Ryszka
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK
| | - R Pandey
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK
| | - D Mészáros
- Department of Experimental Physics, Comenius University in Bratislava Mlynská dolina F2 84248 Bratislava Slovakia
| | - P Limão-Vieira
- Atomic and Molecular Collisions Laboratory, CEFITEC, Department of Physics, FCT - Universidade NOVA de Lisboa P-2829-516 Caparica Portugal
| | - P Papp
- Department of Experimental Physics, Comenius University in Bratislava Mlynská dolina F2 84248 Bratislava Slovakia
| | - N J Mason
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK .,School of Physical Sciences, Ingram Building, University of Kent Canterbury CT2 7NH UK
| | - D Townsend
- Institute of Photonics and Quantum Sciences, Heriot-Watt University Edinburgh EH14 4AS UK.,Institute of Chemical Sciences, Heriot-Watt University Edinburgh EH14 4AS UK
| | - K L Nixon
- School of Life, Health, and Chemical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK.,School of Sciences, University of Wolverhampton Wulfruna Street Wolverhampton WV1 1LY UK
| | - V Vizcaino
- CIMAP UMR 6252, CEA/CNRS/ENSICAEN/Université de Caen Normandie, GANIL Bd Becquerel BP 5133 14070 Caen France
| | - J-C Poully
- CIMAP UMR 6252, CEA/CNRS/ENSICAEN/Université de Caen Normandie, GANIL Bd Becquerel BP 5133 14070 Caen France
| | - S Eden
- School of Physical Sciences, The Open University Walton Hall Milton Keynes MK7 6AA UK
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Paterson MJ, Townsend D. Rydberg-to-valence evolution in excited state molecular dynamics. INT REV PHYS CHEM 2020. [DOI: 10.1080/0144235x.2020.1815389] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
| | - Dave Townsend
- Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, UK
- Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, UK
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