Covariance imaging experiments using a pixel-imaging mass-spectrometry camera

Slater, Craig S.; Blake, S.; Brouard, M.; Lauer, Alexandra; Vallance, Claire; John, J.; Turchetta, R.; Nomerotski, A.; Christensen, Lars Rune; Nielsen, Jens Hedegaard; Johansson, Mikael P.; Stapelfeldt, Henrik

doi:10.1103/physreva.89.011401

Cited by 71 publications

(107 citation statements)

References 32 publications

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“…The PIMMS camera plays a crucial role in the determination of the angle between the Br þ and F þ ions, since it records images of all ionic species for each laser pulse sequence. This allows us to identify correlations between the emission directions of the Br þ and F þ ions through a covariance analysis of the velocity vectors of the recoiling ions [25,26]. The result of the analysis is represented as covariance images of one ion species with respect to the other.…”

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confidence: 99%

“…The cationic fragments, notably Br þ and F þ ions, from the Coulomb explosion were collected in a velocity map imaging system enclosing the interaction region and the velocity focused onto a position sensitive detector consisting of a microchannel plate assembly and a P47 phosphor screen. The phosphor screen was backed by a pixel imaging mass spectrometry (PIMMS) camera [23,24] To image the torsional motion we follow the strategy from previous works [11,13,25] and determine the dihedral angle directly by measuring the angle between the fragmenting Br þ ions and F þ ions. Assuming axial recoil, this is the angle between the Br-and F-substituted benzene rings when the molecule is viewed along the long axis.…”

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Dynamic Stark Control of Torsional Motion by a Pair of Laser Pulses

et al. 2014

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The torsional motion of a molecule composed of two substituted benzene rings, linked by a single bond, is coherently controlled by a pair of strong (3×10^{13} W cm^{-2}), nonresonant (800 nm) 200-fs-long laser pulses-both linearly polarized perpendicular to the single-bond axis. If the second pulse is sent at the time when the two benzene rings rotate toward (away from) each other the amplitude of the torsion is strongly enhanced (reduced). The torsional motion persists for more than 150 ps corresponding to approximately 120 torsional oscillations. Our calculations show that the key to control is the strong transient modification of the natural torsional potential by the laser-induced dynamic Stark effect.

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Dynamic Stark Control of Torsional Motion by a Pair of Laser Pulses

et al. 2014

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“…16,17 Structure characterization has mainly been obtained by IR spectroscopy 22-24 although for complexes of larger molecules this becomes very challenging, as the density of states is too high to clearly resolve peaks in the spectra.Recently, we introduced an alternative method for structure determination of dimers created inside He droplets, namely Coulomb explosion induced by an intense femtosecond (fs) laser pulse and recording of the emission direction of the fragment ions including identification of their angular correlations, 25,26 implemented through covariance analysis. [27][28][29] Crucial to the structure determination was that the dimers had a well-defined spatial orientation prior to the Coulomb explosion event, in practice obtained by laser-induced alignment with a moderately intense laser pulse. 30,31 While the Coulomb explosion method may not match the level of structural accuracy possible with high resolution spectroscopy, at least not for comparatively small molecules, it distinguishes itself by the fact that the structure is captured within the time scale of the pulse duration, i.e.…”

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Structure determination of the tetracene dimer in helium nanodroplets using femtosecond strong-field ionization

Schouder

Chatterley

Calvo

et al. 2019

Structural Dynamics

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Dimers of tetracene molecules are formed inside helium nanodroplets and identified through covariance analysis of the emission directions of kinetic tetracene cations stemming from femtosecond laser-induced Coulomb explosion. Next, the dimers are aligned in either one or three dimensions under field-free conditions by a nonresonant, moderately intense laser pulse. The experimental angular covariance maps of the tetracene ions are compared to calculated covariance maps for seven different dimer conformations and found to be consistent with four of these. Additional measurements of the alignment-dependent strong-field ionization yield of the dimer narrow the possible conformations down to either a slipped-parallel or parallel-slightly rotated structure. According to our quantum chemistry calculations, these are the two most stable gas-phase conformations of the dimer and one of them is favorable for singlet fission.

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“…31,32 Further details of the experimental setup are described elsewhere. 27,28,33 Figure 1 demonstrates the observables acquired from the Coulomb explosion of 3,5-DFIB.…”

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Communication: Gas-phase structural isomer identification by Coulomb explosion of aligned molecules

Burt

Amini

Lee

et al. 2018

The Journal of Chemical Physics

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The gas-phase structures of four difluoroiodobenzene and two dihydroxybromobenzene isomers were identified by correlating the emission angles of atomic fragment ions created following femtosecond laser-induced Coulomb explosion. The structural determinations were facilitated by confining the most polarizable axis of each molecule to the detection plane prior to the Coulomb explosion event using one-dimensional laser-induced adiabatic alignment. For a molecular target consisting of two difluoroiodobenzene isomers, each constituent structure could additionally be singled out and distinguished. a) These authors contributed equally to this work. b) ElectronicLaser-induced molecular Coulomb explosion is the process whereby an intense femtosecond laser pulse detaches several electrons from a molecule, breaking it into cationic fragments. If the axial recoil approximation is satisfied, the created fragment ions recoil along the original bond axes of their parent molecule, allowing laser-induced Coulomb explosions to be used for two purposes: the first concerns how molecules are oriented in space at the instant the laser pulse arrives, and is measured by determining the emission directions of the fragment ions with respect to one or more fixed axes. This method has been used as a probe for a large number of laser-induced alignment and orientation experiments. 1-4 The second concerns molecular structures, which can be identified by correlating the measured fragment momenta. These latter experiments have revealed static molecular geometries and, with femtosecond pump-probe schemes, structural and reaction dynamics. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Coulomb explosion research on diatomic and triatomic molecules has demonstrated that covariance and coincidence analyses are efficient and powerful approaches for identifying the correlations between the emission directions of different fragment ions. 20-25 This is even more evident in studies of larger and more complex molecules, towards which interest has turned over the past decade. 10,16,26,27 Covariance analysis of Coulomb explosion fragments has also been applied to molecules that were pre-aligned by adiabatic laser pulses. [26][27][28] In these experiments, this alignment placed the molecules in well-defined spatial orientations with respect to the imaging detector, and thereby increased the structural information obtained from the recorded fragment momenta. The purpose of this work is to further develop Coulomb explosion imaging of pre-aligned targets as a method to determine the structures of polyatomic molecules. In particular, we demonstrate that four difluoroiodobenzene (DFIB) isomers can be unequivocally distinguished by analyzing the angular correlations of specific fragment ions. Furthermore, we show that for a mixture of two DFIB isomers the constituent structures can be singled out and identified. Finally, to demonstrate that our method is also capable of identifying isomers when only one substituent is a halogen atom, experiments were carr...

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Covariance imaging experiments using a pixel-imaging mass-spectrometry camera

Cited by 71 publications

References 32 publications

Dynamic Stark Control of Torsional Motion by a Pair of Laser Pulses

Dynamic Stark Control of Torsional Motion by a Pair of Laser Pulses

Structure determination of the tetracene dimer in helium nanodroplets using femtosecond strong-field ionization

Communication: Gas-phase structural isomer identification by Coulomb explosion of aligned molecules

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