Publications

@article{doi:10.1021/jacs.4c01543,

title = {Direct Observation of a Roaming Intermediate and Its Dynamics},

author = {Grite L. Abma and Michael A. Parkes and Weronika O. Razmus and Yu Zhang and Adam S. Wyatt and Emma Springate and Richard T. Chapman and Daniel A. Horke and Russell S. Minns},

doi = {10.1021/jacs.4c01543},

year  = {2024},

date = {2024-04-29},

urldate = {2024-04-29},

journal = {J. Am. Chem. Soc.},

volume = {146},

number = {18},

pages = {12595-12600},

keywords = {dynamics, experimental design, HHG, intramolecular interactions, Non-adiabatic dynamics, Photoelectron spectroscopy},

pubstate = {published},

tppubtype = {article}

}

@article{doi:10.1021/acs.jpclett.4c00768,

title = {Preparation of Tautomer-Pure Molecular Beams by Electrostatic Deflection},

author = {Grite L. Abma and Michael A. Parkes and Daniel A. Horke},

doi = {10.1021/acs.jpclett.4c00768},

year  = {2024},

date = {2024-04-24},

urldate = {2024-04-24},

journal = {J. Phys. Chem. Lett.},

volume = {15},

number = {17},

pages = {4587-4592},

keywords = {Control, electrostatic deflector, experimental design, Isomer-effects, photoelectron imaging, Photoelectron spectroscopy},

pubstate = {published},

tppubtype = {article}

}

@article{ROTH2024168820,

title = {New aerodynamic lens injector for single particle diffractive imaging},

author = {Nils Roth and Daniel A. Horke and Jannik L\"{u}bke and Amit K. Samanta and Armando D. Estillore and Lena Worbs and Nicolai Pohlman and Kartik Ayyer and Andrew Morgan and Holger Fleckenstein and Martin Domaracky and Benjamin Erk and Christopher Passow and Jonathan Correa and Oleksandr Yefanov and Anton Barty and Sa\v{s}a Bajt and Richard A. Kirian and Henry N. Chapman and Jochen K\"{u}pper},

url = {https://www.sciencedirect.com/science/article/pii/S0168900223008112},

doi = {https://doi.org/10.1016/j.nima.2023.168820},

issn = {0168-9002},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment},

volume = {1058},

pages = {168820},

abstract = {An aerodynamic lens injector was developed specifically for the needs of single-particle diffractive imaging experiments at free-electron lasers. Its design allows for quick changes of injector geometries and focusing properties in order to optimize injection for specific individual samples. Here, we present results of its first use at the FLASH free-electron-laser facility. Recorded diffraction patterns of polystyrene spheres are modeled using Mie scattering, which allowed for the characterization of the particle beam under diffractive-imaging conditions and yielded good agreement with particle-trajectory simulations. The complex refractive index of polystyrene at λ=4.5nm was determined as m=0.976−0.001i.},

keywords = {crystallography, diffractive imaging, experimental design, nanoparticles, Simulation, Single-particle imaging, XFEL},

pubstate = {published},

tppubtype = {article}

}

@article{dauletyarovVaporizationIntactNeutral2023,

title = {Vaporization of Intact Neutral Biomolecules Using Laser-Based Thermal Desorption},

author = {Yerbolat Dauletyarov and Siwen Wang and Daniel A. Horke},

url = {https://pubs.acs.org/doi/10.1021/jasms.3c00194},

doi = {10.1021/jasms.3c00194},

issn = {1044-0305, 1879-1123},

year  = {2023},

date = {2023-06-01},

urldate = {2023-06-01},

journal = {J. Am. Soc. Mass Spectrom.},

volume = {34},

pages = {1538},

abstract = {The production of a clean neutral molecular sample is a crucial step in many gas-phase spectroscopy and reaction dynamics experiments investigating neutral species. Unfortunately, conventional methods based on heating cannot be used with most nonvolatile biomolecules due to their thermal instability. In this paper, we demonstrate the application of laser-based thermal desorption (LBTD) to produce neutral molecular plumes of biomolecules such as dipeptides and lipids. Specifically, we report mass spectra of glycylglycine, glycyl-L-alanine, and cholesterol obtained using LBTD vaporization, followed by soft femtosecond multiphoton ionization (fs-MPI) at 400 nm. For all molecules, the signal from the intact precursor ion was observed, highlighting the softness and applicability of the LBTD and fs-MPI approach. In more detail, cholesterol underwent hardly any fragmentation. Both dipeptides fragmented significantly, although mostly through only a single channel, which we attribute to the fs-MPI process.},

keywords = {experimental design, LBTD, photofragmentation},

pubstate = {published},

tppubtype = {article}

}

@article{D3CP00328K,

title = {High-throughput UV-photofragmentation studies of thymine and guanine},

author = {Siwen Wang and Yerbolat Dauletyarov and Peter Kr\"{u}ger and Daniel A. Horke},

url = {http://dx.doi.org/10.1039/D3CP00328K},

doi = {10.1039/D3CP00328K},

year  = {2023},

date = {2023-04-15},

urldate = {2023-01-01},

journal = {Phys. Chem. Chem. Phys.},

volume = {25},

pages = {12322},

publisher = {The Royal Society of Chemistry},

abstract = {High-throughput photofragmentation studies of thymine and guanine were performed at 257 and 343 nm and for a wide range of ionisation laser intensities. Combining a continuous laser-based thermal desorption source with femtosecond multiphoton ionisation using a 50 kHz repetition rate laser allowed us to produce detailed 2D maps of fragmentation as a function of incident laser intensity. The fragmentation was distinctly soft, the parent ions being at least an order of magnitude more abundant than fragment ions. For thymine there was a single dominant fragmentation channel, which involves consecutive HNCO and CO losses. In contrast, for guanine there were several competing ones, the most probable channel corresponding to CH2N2 loss through opening of the pyrimidine ring. The dependence of parent ion abundance on the ionisation laser intensity showed that at 257 nm the ionisation of thymine is a 1 + 1 resonance enhanced process through its open-shell singlet state.},

keywords = {experimental design, LBTD, photofragmentation},

pubstate = {published},

tppubtype = {article}

}

@article{wangComparingPulsedContinuous2022,

title = {Comparing Pulsed and Continuous Laser-Induced Acoustic Desorption (LIAD) as Sources for Intact Biomolecules},

author = {Siwen Wang and Grite L. Abma and Peter Kr\"{u}ger and Andre Roij and Michiel Balster and Niek Janssen and Daniel A. Horke},

url = {https://link.springer.com/10.1140/epjd/s10053-022-00459-7},

doi = {10.1140/epjd/s10053-022-00459-7},

issn = {1434-6060, 1434-6079},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

journal = {Eur. Phys. J. D},

volume = {76},

number = {7},

pages = {128},

abstract = {A major obstacle to the gas-phase study of larger (bio)molecular systems is the vaporisation step, that is, the introduction of intact sample molecules into the gas-phase. A promising approach is the use of laser-induced acoustic desorption (LIAD) sources, which have been demonstrated using both nanosecond pulsed and continuous desorption lasers. We directly compare here both approaches for the first time under otherwise identical conditions using adenine as a prototypical biological molecule, and study the produced molecular plumes using femtosecond multiphoton ionisation. We observe different desorption mechanisms at play for the two different desorption laser sources; however, we find no evidence in either case that the desorption process leads to fragmentation of the target molecule unless excessive desorption energy is applied. This makes LIAD a powerful approach for techniques that require high density and high purity samples in the gas-phase, such as ultrafast dynamics studies or diffraction experiments.},

keywords = {experimental design, LBTD, photofragmentation},

pubstate = {published},

tppubtype = {article}

}

@article{abmaSinglecolorIsomerresolvedSpectroscopy2022,

title = {Single-Color Isomer-Resolved Spectroscopy},

author = {Grite L. Abma and Dries Kleuskens and Siwen Wang and Michiel Balster and Andre Roij and Niek Janssen and Daniel A. Horke},

url = {https://doi.org/10.1021/acs.jpca.2c02277},

doi = {10.1021/acs.jpca.2c02277},

year  = {2022},

date = {2022-06-01},

urldate = {2022-06-01},

journal = {The Journal of Physical Chemistry A},

volume = {126},

pages = {3811\textendash3815},

abstract = {Structural isomers, such as conformers or tautomers, are

of significant importance across chemistry and biology, as they can have

different functionalities. In gas-phase experiments using molecular

beams, formation of many different isomers cannot be prevented, and

their presence significantly complicates the assignment of spectral lines.

Current isomer-resolved spectroscopic techniques heavily rely on

theoretical calculations or make use of elaborate double-resonance

schemes. We show here that isomer-resolved spectroscopy can also be

performed using a single tunable laser. In particular, we demonstrate

single-color isomer-resolved spectroscopy by utilizing electrostatic

deflection to spatially separate the isomers. We show that for 3-

aminophenol we can spatially separate the syn and anti conformers and

use these pure samples to perform high-resolution REMPI spectroscopy, making the assignment of transitions to a particular isomer trivial, without any additional a priori information. This approach allows one to add isomer specificity to any molecular-beam-based experiment.},

keywords = {Control, electrostatic deflector, experimental design, Isomer-effects},

pubstate = {published},

tppubtype = {article}

}

@article{Samanta:StructuralDynamics7:024304,

title = {Controlled Beams of Shock-Frozen, Isolated, Biological and Artificial Nanoparticles},

author = {Amit K. Samanta and Muhamed Amin and Armando D. Estillore and Nils Roth and Lena Worbs and Daniel A. Horke and Jochen K\"{u}pper},

url = {https://aca.scitation.org/doi/10.1063/4.0000004},

doi = {10.1063/4.0000004},

year  = {2020},

date = {2020-03-01},

urldate = {2020-07-21},

journal = {Structural Dynamics},

volume = {7},

number = {2},

pages = {024304},

publisher = {American Institute of Physics},

abstract = {X-ray free-electron lasers promise diffractive imaging of single molecules and nanoparticles with atomic spatial resolution. This relies on the averaging of millions of diffraction patterns of identical particles, which should ideally be isolated in the gas phase and preserved in their native structure. Here, we demonstrated that polystyrene nanospheres and Cydia pomonella granulovirus can be transferred into the gas phase, isolated, and very quickly shock-frozen, i.e., cooled to 4,K within microseconds in a helium-buffer-gas cell, much faster than state-of-the-art approaches. Nanoparticle beams emerging from the cell were characterized using particle-localization microscopy with light-sheet illumination, which allowed for the full reconstruction of the particle beams, focused to $\<$100$mu$m$\<$100,$mu$m$\<$math display="inline" overflow="scroll" altimg="eq-00001.gif"$\>$ $\<$mrow$\>$ $\<$mo$\>\&$lt;$\<$/mo$\>$ $\<$mn$\>$100$\<$/mn$\>$ $\<$mo$\>$,$\<$/mo$\>$ $\<$mi$\>mu\<$/mi$\>$ $\<$mi mathvariant="normal"$\>$m$\<$/mi$\>\<$/mrow$\>\<$/math$\>$, as well as for the determination of particle flux and number density. The experimental results were quantitatively reproduced and rationalized through particle-trajectory simulations. We propose an optimized setup with cooling rates for particles of few-nanometers on nanosecond timescales. The produced beams of shock-frozen isolated nanoparticles provide a breakthrough in sample delivery, e.g., for diffractive imaging and microscopy or low-temperature nanoscience.},

keywords = {Control, experimental design, nanoparticles},

pubstate = {published},

tppubtype = {article}

}

@article{Worbs:Opt.Express27:36580,

title = {Light-Sheet Imaging for the Recording of Transverse Absolute Density Distributions of Gas-Phase Particle-Beams from Nanoparticle Injectors},

author = {Lena Worbs and Lena Worbs and Jannik L\"{u}bke and Jannik L\"{u}bke and Jannik L\"{u}bke and Nils Roth and Nils Roth and Amit K. Samanta and Daniel A. Horke and Daniel A. Horke and Daniel A. Horke and Jochen K\"{u}pper and Jochen K\"{u}pper and Jochen K\"{u}pper},

url = {https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-25-36580},

doi = {10.1364/OE.27.036580},

issn = {1094-4087},

year  = {2019},

date = {2019-12-01},

urldate = {2020-07-21},

journal = {Opt. Express},

volume = {27},

number = {25},

pages = {36580--36586},

publisher = {Optical Society of America},

abstract = {Imaging biological molecules in the gas-phase requires novel sample delivery methods, which generally have to be characterized and optimized to produce high-density particle beams. A non-destructive characterization method of the transverse particle beam profile is presented. It enables the characterization of the particle beam in parallel to the collection of, for instance, x-ray-diffraction patterns. As a rather simple experimental method, it requires the generation of a small laser-light sheet using a cylindrical telescope and a microscope. The working principle of this technique was demonstrated for the characterization of the fluid-dynamic-focusing behavior of 220 nm polystyrene beads as prototypical nanoparticles. The particle flux was determined and the velocity distribution was calibrated using Mie-scattering calculations.},

keywords = {experimental design, nanoparticles, Single-particle imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Roth:JournalofAerosolScience124:17,

title = {Optimizing Aerodynamic Lenses for Single-Particle Imaging},

author = {Nils Roth and Salah Awel and Daniel A. Horke and Jochen K\"{u}pper},

url = {http://www.sciencedirect.com/science/article/pii/S0021850217304652},

doi = {10.1016/j.jaerosci.2018.06.010},

issn = {0021-8502},

year  = {2018},

date = {2018-10-01},

urldate = {2019-01-15},

journal = {Journal of Aerosol Science},

volume = {124},

pages = {17--29},

abstract = {A numerical simulation infrastructure capable of calculating the flow of gas and the trajectories of particles through an aerodynamic lens injector is presented. The simulations increase the fundamental understanding and predict optimized injection geometries and parameters. Our simulation results were compared to previous reports and also validated against experimental data for 500 nm polystyrene spheres from an aerosol-beam-characterization setup. The simulations yielded a detailed understanding of the radial phase-space distribution and highlighted weaknesses of current aerosol injectors for single-particle diffractive imaging. With the aid of these simulations we developed new experimental implementations to overcome current limitations.},

keywords = {experimental design, nanoparticles, Simulation, Single-particle imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Wiedorn:IUCrJ5:574,

title = {Rapid Sample Delivery for Megahertz Serial Crystallography at X-Ray FELs},

author = {M. O. Wiedorn and S. Awel and A. J. Morgan and K. Ayyer and Y. Gevorkov and H. Fleckenstein and N. Roth and L. Adriano and R. Bean and K. R. Beyerlein and J. Chen and J. Coe and F. Cruz-Mazo and T. Ekeberg and R. Graceffa and M. Heymann and D. A. Horke and J. Knov ska and V. Mariani and R. Nazari and D. Oberth\"{u}r and A. K. Samanta and R. G. Sierra and C. A. Stan and O. Yefanov and D. Rompotis and J. Correa and B. Erk and R. Treusch and J. Schulz and B. G. Hogue and A. M. Ga n\'{a}n-Calvo and P. Fromme and J. K\"{u}pper and A. V. Rode and S. Bajt and R. A. Kirian and H. N. Chapman},

url = {http://scripts.iucr.org/cgi-bin/paper?it5016},

doi = {10.1107/S2052252518008369},

issn = {2052-2525},

year  = {2018},

date = {2018-09-01},

urldate = {2019-01-24},

journal = {IUCrJ},

volume = {5},

number = {5},

pages = {574--584},

abstract = {Liquid microjets are a common means of delivering protein crystals to the focus of X-ray free-electron lasers (FELs) for serial femtosecond crystallography measurements. The high X-ray intensity in the focus initiates an explosion of the microjet and sample. With the advent of X-ray FELs with megahertz rates, the typical velocities of these jets must be increased significantly in order to replenish the damaged material in time for the subsequent measurement with the next X-ray pulse. This work reports the results of a megahertz serial diffraction experiment at the FLASH FEL facility using 4.3hspace0.25emnm radiation. The operation of gas-dynamic nozzles that produce liquid microjets with velocities greater than 80hspace0.25emmhspace0.25ems-1 was demonstrated. Furthermore, this article provides optical images of X-ray-induced explosions together with Bragg diffraction from protein microcrystals exposed to trains of X-ray pulses repeating at rates of up to 4.5hspace0.25emMHz. The results indicate the feasibility for megahertz serial crystallography measurements with hard X-rays and give guidance for the design of such experiments.},

keywords = {crystallography, diffractive imaging, experimental design, Single-particle imaging, XFEL},

pubstate = {published},

tppubtype = {article}

}

@article{Singh:Phys.Rev.A97:032704,

title = {Optimized Cell Geometry for Buffer-Gas-Cooled Molecular-Beam Sources},

author = {Vijay Singh and Amit K Samanta and Nils Roth and Daniel Gusa and Tim Ossenbr\"{u}ggen and Igor Rubinsky and Daniel A Horke and Jochen K\"{u}pper},

url = {https://link.aps.org/doi/10.1103/PhysRevA.97.032704},

doi = {10.1103/PhysRevA.97.032704},

year  = {2018},

date = {2018-03-01},

journal = {Phys. Rev. A},

volume = {97},

number = {3},

pages = {032704},

abstract = {We have designed, constructed, and commissioned a cryogenic helium buffer-gas source for producing a cryogenically cooled molecular beam and evaluated the effect of different cell geometries on the intensity of the produced molecular beam, using ammonia as a test molecule. Planar and conical entrance and exit geometries are tested. We observe a threefold enhancement in the $textbackslash mathrmNH_3$ signal for a cell with planar entrance and conical-exit geometry, compared to that for a typically used ``boxlike'' geometry with planar entrance and exit. These observations are rationalized by flow field simulations for the different buffer-gas cell geometries. The full thermalization of molecules with the helium buffer gas is confirmed through rotationally resolved resonance-enhanced multiphoton ionization spectra yielding a rotational temperature of 5 K.},

keywords = {Control, experimental design},

pubstate = {published},

tppubtype = {article}

}

@article{Huang:Anal.Chem.90:3920,

title = {Development and Characterization of a Laser-Induced Acoustic Desorption Source},

author = {Zhipeng Huang and Tim Ossenbr\"{u}ggen and Igor Rubinsky and Matthias Schust and Daniel A Horke and Jochen K\"{u}pper},

url = {http://pubs.acs.org/doi/10.1021/acs.analchem.7b04797},

doi = {10.1021/acs.analchem.7b04797},

year  = {2018},

date = {2018-02-01},

journal = {Anal. Chem.},

volume = {90},

number = {6},

pages = {3920--3927},

keywords = {experimental design, LIAD},

pubstate = {published},

tppubtype = {article}

}

@article{Wiedorn:JSynchrotronRad24:1296,

title = {Post-Sample Aperture for Low Background Diffraction Experiments at X-Ray Free-Electron Lasers},

author = {M. O. Wiedorn and S. Awel and A. J. Morgan and M. Barthelmess and R. Bean and K. R. Beyerlein and L. M. G. Chavas and N. Eckerskorn and H. Fleckenstein and M. Heymann and D. A. Horke and J. Knov ska and V. Mariani and D. Oberth\"{u}r and N. Roth and O. Yefanov and A. Barty and S. Bajt and J. K\"{u}pper and A. V. Rode and R. A. Kirian and H. N. Chapman},

url = {http://scripts.iucr.org/cgi-bin/paper?gb5058},

doi = {10.1107/S1600577517011961},

issn = {1600-5775},

year  = {2017},

date = {2017-11-01},

urldate = {2019-01-24},

journal = {J Synchrotron Rad},

volume = {24},

number = {6},

pages = {1296--1298},

abstract = {The success of diffraction experiments from weakly scattering samples strongly depends on achieving an optimal signal-to-noise ratio. This is particularly important in single-particle imaging experiments where diffraction signals are typically very weak and the experiments are often accompanied by significant background scattering. A simple way to tremendously reduce background scattering by placing an aperture downstream of the sample has been developed and its application in a single-particle X-ray imaging experiment at FLASH is demonstrated. Using the concept of a post-sample aperture it was possible to reduce the background scattering levels by two orders of magnitude.},

keywords = {experimental design, Single-particle imaging, XFEL},

pubstate = {published},

tppubtype = {article}

}

@article{Teschmit:J.Chem.Phys.147:144204,

title = {Characterizing and Optimizing a Laser-Desorption Molecular Beam Source},

author = {Nicole Teschmit and Karol D\lugo\l\k{e}cki and Daniel Gusa and Igor Rubinsky and Daniel A Horke and Jochen K\"{u}pper},

url = {http://aip.scitation.org/doi/10.1063/1.4991639},

doi = {10.1063/1.4991639},

year  = {2017},

date = {2017-10-01},

journal = {J. Chem. Phys.},

volume = {147},

number = {14},

pages = {144204},

abstract = {The design and characterization of a new laser-desorption molecular beam source, tailored for use in x-ray free-electron laser and ultrashort-pulse laser imaging experiments, is presented. It consists of a single mechanical unit containing all source components, including the molecular-beam valve, the sample, and the fiber-coupled desorption laser, which is movable in five axes, as required for experiments at central facilities. Utilizing strong-field ionization, we characterize the produced molecular beam and evaluate the influence of desorption laser pulse energy, relative timing of valve opening and desorption laser, sample bar height, and which part of the molecular packet is probed on the sample properties. Strong-field ionization acts as a universal probe and allows detecting all species present in the molecular beam, and hence enables us to analyze the purity of the produced molecular beam, including molecular fragments. We present optimized experimental parameters for the production of the purest ...},

keywords = {experimental design},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:JournalofAppliedPhysics121:123106,

title = {Characterizing Gas Flow from Aerosol Particle Injectors},

author = {Daniel A Horke and Nils Roth and Lena Worbs and Jochen K\"{u}pper},

url = {http://aip.scitation.org/doi/10.1063/1.4978914},

doi = {10.1063/1.4978914},

year  = {2017},

date = {2017-03-01},

journal = {Journal of Applied Physics},

volume = {121},

number = {12},

pages = {123106},

keywords = {experimental design, nanoparticles},

pubstate = {published},

tppubtype = {article}

}

@article{Awel:OpticsExpress24:6507,

title = {Visualizing Aerosol-Particle Injection for Diffractive-Imaging Experiments},

author = {Salah Awel and Richard A Kirian and Niko Eckerskorn and Max Wiedorn and Daniel A Horke and Andrei V Rode and Jochen K\"{u}pper and Henry N Chapman},

url = {http://www.osapublishing.org/viewmedia.cfm?uri=oe-24-6-6507\&seq=0\&html=true},

doi = {10.1364/OE.24.006507},

year  = {2016},

date = {2016-03-01},

journal = {Optics Express},

volume = {24},

number = {6},

pages = {6507--6521},

abstract = {Delivering sub-micrometer particles to an intense x-ray focus is a crucial aspect of single-particle diffractive-imaging experiments at x-ray free-electron lasers. Enabling direct visualization of sub-micrometer aerosol particle streams without interfering with the operation of the particle injector can greatly improve the overall efficiency of single-particle imaging experiments by reducing the amount of time and sample consumed during measurements. We have developed in-situ non-destructive imaging diagnostics to aid real-time particle injector optimization and x-ray/particle-beam alignment, based on laser illumination schemes and fast imaging detectors. Our diagnostics are constructed to provide a non-invasive rapid feedback on injector performance during measurements, and have been demonstrated during diffraction measurements at the FLASH free-electron laser.},

keywords = {diffractive imaging, experimental design, nanoparticles},

pubstate = {published},

tppubtype = {article}

}

@article{Kirian:StructuralDynamics2:041717,

title = {Simple Convergent-Nozzle Aerosol Injector for Single-Particle Diffractive Imaging with X-Ray Free-Electron Lasers},

author = {R A Kirian and S Awel and N Eckerskorn and H Fleckenstein and M Wiedorn and L Adriano and S Bajt and M Barthelmess and R Bean and K R Beyerlein and L M G Chavas and M Domaracky and M Heymann and D A Horke and J Knoska and M Metz and A Morgan and D Oberthuer and N Roth and T Sato and P L Xavier and O Yefanov and A V Rode and J Kupper and H N Chapman},

url = {http://scitation.aip.org/content/aca/journal/sdy/2/4/10.1063/1.4922648},

doi = {10.1063/1.4922648},

year  = {2015},

date = {2015-07-01},

journal = {Structural Dynamics},

volume = {2},

number = {4},

pages = {041717},

keywords = {diffractive imaging, experimental design, nanoparticles, Single-particle imaging, XFEL},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:Rev.Sci.Instr.83:063101,

title = {Velocity-Map Imaging at Low Extraction Fields.},

author = {Daniel A Horke and Gareth M Roberts and Julien Lecointre and Jan R R Verlet},

url = {http://link.aip.org/link/RSINAK/v83/i6/p063101/s1\&Agg=doi},

doi = {10.1063/1.4724311},

year  = {2012},

date = {2012-01-01},

journal = {Rev. Sci. Instr.},

volume = {83},

number = {6},

pages = {063101},

abstract = {We present a velocity-map imaging (VMI) setup for photoelectron imaging that utilizes low electric extraction fields. This avoids any complications that could arise from electrostatic interactions between the extraction field and the molecular properties that are probed and has a minimal effect on the trajectory of ions in ion beam experiments. By using an attractive potential supplied to the detector, and keeping the electrodes at ground (zero) potential, we show that fringe fields between the VMI arrangement and the vacuum chamber can be eliminated, which is important in experiments on ions.},

keywords = {experimental design, photoelectron imaging, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Lecointre:J.Phys.Chem.A114:11216,

title = {Ultrafast Relaxation Dynamics Observed Through Time-Resolved Photoelectron Angular Distributions textdagger},

author = {Julien Lecointre and Gareth M Roberts and Daniel A Horke and Jan R R Verlet},

url = {http://pubs.acs.org/doi/abs/10.1021/jp1028855},

doi = {10.1021/jp1028855},

year  = {2010},

date = {2010-10-01},

journal = {J. Phys. Chem. A},

volume = {114},

number = {42},

pages = {11216--11224},

abstract = {Time-resolved photoelectron imaging of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion is presented. Photoelectron angular distributions (PADs) are qualitatively analyzed in terms of the simple s-p model that is based on symmetry arguments. The internal conversion dynamics from the first excited state (1(2)B(3u)) to the ground state ((2)B(2g)) may be observed through temporal changes in the PADs of the spectrally overlapping photoelectron features arising from photodetachment of the ground state and the excited state. A formulism for extracting the population dynamics from the $beta$(2) anisotropy parameter of overlapping spectroscopic features is presented. This is used to extract the lifetime of the first excited state, which is in good agreement with that observed in the time-resolved photoelectron spectra.},

keywords = {Anion spectroscopy, experimental design, photoelectron imaging, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}