Publications

@article{caballoDisentanglingMultiphotonIonization2023,

title = {Disentangling Multiphoton Ionization and Dissociation Channels in Molecular Oxygen Using Photoelectron\textendashPhotoion Coincidence Imaging},

author = {Ana Caballo and Anders J. T. M. Huits and David H. Parker and Daniel A. Horke},

url = {https://pubs.acs.org/doi/10.1021/acs.jpca.2c06707},

doi = {10.1021/acs.jpca.2c06707},

issn = {1089-5639, 1520-5215},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

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

volume = {127},

number = {1},

pages = {92--98},

abstract = {Multiphoton excitation of molecular oxygen in the 392-408 nm region is studied using a tunable femtosecond laser coupled with a double velocity map imaging photoelectron- photoion coincidence spectrometer. The laser intensity is held at $\leqsim$1 TW/cm2 to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O2+ production is found to be resonance enhanced around 400 nm via three-photon excitation to the e$'$3$Delta$u(v = 0) state, similar to results from REMPI studies using nanosecond dye lasers. O+ production reaches 7% of the total ion yield around 405 nm due to two processes: autoionization following five-photon excitation of O2, producing O2+(X(v)) in a wide range of vibrational states followed by two- or three-photon dissociation, or six-photon excitation to a superexcited O2** state followed by neutral dissociation and subsequent ionization of the electronically excited O atom. Coincidence detection is shown to be crucial in identifying these competing pathways.},

keywords = {Coincidence Imaging, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Caballo:J.Phys.Chem.A125:9060,

title = {Femtosecond 2 + 1 Resonance-Enhanced Multiphoton Ionization Spectroscopy of the C-State in Molecular Oxygen},

author = {Ana Caballo and Anders J. T. M. Huits and Arno Vredenborg and Michiel Balster and David H. Parker and Daniel A. Horke},

url = {https://doi.org/10.1021/acs.jpca.1c05541},

doi = {10.1021/acs.jpca.1c05541},

issn = {1089-5639},

year  = {2021},

date = {2021-10-01},

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

volume = {125},

number = {41},

pages = {9060--9064},

publisher = {American Chemical Society},

abstract = {Coincidence electron-cation imaging is used to characterize the multiphoton ionization of O2 via the v = 4,5 levels of the 3s(3$Pi$g) Rydberg state. A tunable 100 fs laser beam operating in the 271\textendash 263 nm region is found to cause a nonresonant ionization across this wavelength range, with an additional resonant ionization channel only observed when tuned to the 3$Pi$g(v = 5) level. A distinct 3s textrightarrow p wave character is observed in the photoelectron angular distribution for the v = 5 channel when on resonance.},

keywords = {Coincidence Imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Bellshaw:Chem.Phys.Lett.683:383,

title = {Ab-Initio Surface Hopping and Multiphoton Ionisation Study of the Photodissociation Dynamics of CS2},

author = {Darren Bellshaw and Daniel A. Horke and Adam D. Smith and Hannah M. Watts and Edward Jager and Emma Springate and Oliver Alexander and Cephise Cacho and Richard T. Chapman and Adam Kirrander and Russell S. Minns},

url = {http://www.sciencedirect.com/science/article/pii/S0009261417301744},

doi = {10.1016/j.cplett.2017.02.058},

issn = {0009-2614},

year  = {2017},

date = {2017-09-01},

urldate = {2019-01-24},

journal = {Chem. Phys. Lett.},

volume = {683},

pages = {383--388},

series = {Ahmed Zewail (1946-2016) Commemoration Issue of Chemical Physics Letters},

abstract = {New ab initio surface hopping simulations of the excited state dynamics of CS2 including spin-orbit coupling are compared to new experimental measurements using a multiphoton ionisation probe in a photoelectron spectroscopy experiment. The calculations highlight the importance of the triplet states even in the very early time dynamics of the dissociation process and allow us to unravel the signatures in the experimental spectrum, linking the observed changes to both electronic and nuclear degrees of freedom within the molecule.},

keywords = {dynamics, Non-adiabatic dynamics, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:Phys.Rev.Lett.117:163002,

title = {Hydrogen Bonds in Excited State Proton Transfer},

author = {D A Horke and H M Watts and A D Smith and E Jager and E Springate and O Alexander and C Cacho and R T Chapman and R S Minns},

url = {http://link.aps.org/doi/10.1103/PhysRevLett.117.163002},

doi = {10.1103/PhysRevLett.117.163002},

year  = {2016},

date = {2016-10-01},

journal = {Phys. Rev. Lett.},

volume = {117},

number = {16},

pages = {163002},

abstract = {Hydrogen bonding may safeguard biomolecules against the damaging effects of UV light.},

keywords = {Coincidence Imaging, intramolecular interactions, Isomer-effects, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Smith:Phys.Chem.Chem.Phys.18:28150,

title = {Resonant Multiphoton Ionisation Probe of the Photodissociation Dynamics of Ammonia},

author = {Adam D Smith and Hannah M Watts and Edward Jager and Daniel A Horke and Emma Springate and Oliver Alexander and Cephise Cacho and Richard T Chapman and Russell S Minns},

url = {http://pubs.rsc.org/en/content/articlehtml/2016/cp/c6cp05279g},

doi = {10.1039/C6CP05279G},

year  = {2016},

date = {2016-10-01},

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

volume = {18},

number = {40},

pages = {28150--28156},

abstract = {The dissociation dynamics of the ~A-state of ammonia have been studied using a resonant multiphoton ionisation probe in a photoelectron spectroscopy experiment. The use of a resonant intermediate in the multiphoton ionisation process changes the ionisation propensity, allowing access to different ion states when compared with equivalent single photon ionisation experiments. Ionisation through the E$'$ 1A1$'$ Rydberg intermediate means we maintain overlap with the ion state for an extended period, allowing us to monitor the excited state population for several hundred femtoseconds. The vibrational states in the photoelectron spectrum show two distinct timescales, 200 fs and 320 fs, that we assign to the non-adiabatic and adiabatic dissociation processes respectively. The different timescales derive from differences in the wavepacket trajectories for the two dissociation pathways that resonantly excite different vibrational states in the intermediate Rydberg state. The timescales are similar to those obtained from time resolved ion kinetic energy release measurements, suggesting we can measure the different trajectories taken out to the region of conical intersection.},

keywords = {dynamics, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Rothhardt:OpticsExpress24:18133,

title = {High-Repetition-Rate and High-Photon-Flux 70 eV High-Harmonic Source for Coincidence Ion Imaging of Gas-Phase Molecules},

author = {Jan Rothhardt and Steffen H\"{a}drich and Yariv Shamir and Maxim Tschnernajew and Robert Klas and Armin Hoffmann and Getnet K Tadesse and Arno Klenke and Thomas Gottschall and Tino Eidam and Jens Limpert and Andreas T\"{u}nnermann and Rebecca Boll and Cedric Bomme and Hatem Dachraoui and Benjamin Erk and Michele Di Fraia and Daniel A Horke and Thomas Kierspel and Terence Mullins and Andreas Przystawik and Evgeny Savelyev and Joss Wiese and Tim Laarmann and Jochen K\"{u}pper and Daniel Rolles},

url = {https://www.osapublishing.org/abstract.cfm?URI=oe-24-16-18133},

doi = {10.1364/OE.24.018133},

year  = {2016},

date = {2016-01-01},

journal = {Optics Express},

volume = {24},

number = {16},

pages = {18133--18147},

abstract = {Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 1011 photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH3I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses.},

keywords = {Coincidence Imaging, HHG, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:J.Phys.Chem.Lett.6:189,

title = {Time-Resolved Photodetachment Anisotropy: Gas-Phase Rotational and Vibrational Dynamics of the Fluorescein Anion},

author = {Daniel A Horke and Adam S Chatterley and James N Bull and Jan R R Verlet},

url = {http://pubs.acs.org/doi/abs/10.1021/jz5022526},

doi = {10.1021/jz5022526},

year  = {2015},

date = {2015-01-01},

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

volume = {6},

number = {1},

pages = {189--194},

abstract = {The photoelectron signal of the singly deprotonated fluorescein anion is found to be highly dependent on the relative polarization between pump and probe pulses, and time-resolved photodetachment anisotropy (TR-PA) is developed as a probe of the rotational dynamics of the chromophore. The total photoelectron signal shows both rotational and vibrational wavepacket dynamics, and we demonstrate how TR-PA can readily disentangle these dynamical processes. TR-PA in fluorescein presents specific opportunities for its development as a probe for rotational dynamics in large biomolecules as fluorescein derivatives are commonly incorporated in complex biomolecules and have been used extensively in time-resolved fluorescence anisotropy measurements, to which TR-PA is a gas-phase analogue.},

keywords = {alignment, Anion spectroscopy, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Chatterley:Phys.Chem.Chem.Phys.16:489,

title = {Effects of Resonant Excitation, Pulse Duration and Intensity on Photoelectron Imaging of a Dianion},

author = {Adam S Chatterley and Daniel A Horke and Jan R R Verlet},

url = {http://xlink.rsc.org/?DOI=c3cp53235f},

doi = {10.1039/c3cp53235f},

year  = {2014},

date = {2014-01-01},

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

volume = {16},

number = {2},

pages = {489--496},

abstract = {The photoelectron imaging of the indigo carmine dianion is used to demonstrate the effects of resonance excitation, pulse duration and pulse intensity on the photoelectron spectra and angular distributions of a dianion. Excitation of the S1 state leads to an aligned distribution of excited state dianions. The photoelectron angular distribution following subsequent photodetachment within a femtosecond laser pulse is primarily determined by the repulsive Coulomb barrier. Extending the timescale for photodetachment to nanoseconds leads to dramatic changes in both the spectral and angular distributions. These observations are explained in terms of statistical detachment of electrons, either from the monoanion, or from the ground state of the dianion following a number of photon cycles through the S1 $\leftarrow$ S0 transition. At high intensity, new electron emission channels open up, leading to emission below the repulsive Coulomb barrier. This has been assigned to strong-field induced detachment and the effect of an electric field on the Coulomb barrier is discussed in terms of the photoelectron spectra and angular distributions.},

keywords = {Anion spectroscopy, photoelectron imaging, Photoelectron spectroscopy, polyanions, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:NatureChem.5:711,

title = {Ultrafast Above-Threshold Dynamics of the Radical Anion of a Prototypical Quinone Electron-Acceptor},

author = {Daniel A Horke and Quansong Li and Llu A Blancafort and Jan R R Verlet},

url = {http://dx.doi.org/10.1038/nchem.1705},

doi = {10.1038/nchem.1705},

year  = {2013},

date = {2013-09-01},

urldate = {2013-09-01},

journal = {Nature Chem.},

volume = {5},

number = {8},

pages = {711--717},

keywords = {dynamics, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:J.Chem.Phys.139:084302,

title = {Influence of the Repulsive Coulomb Barrier on Photoelectron Spectra and Angular Distributions in a Resonantly Excited Dianion},

author = {Daniel A Horke and Adam S Chatterley and Jan R R Verlet},

url = {http://dx.doi.org/10.1063/1.4818597},

doi = {10.1063/1.4818597},

year  = {2013},

date = {2013-01-01},

journal = {J. Chem. Phys.},

volume = {139},

number = {8},

pages = {084302--10},

keywords = {Anion spectroscopy, photoelectron imaging, Photoelectron spectroscopy, polyanions, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Mooney:Chem.Sci.4:921,

title = {Taking the Green Fluorescence out of the Protein: Dynamics of the Isolated GFP Chromophore Anion},

author = {Ciar\'{a}n R S Mooney and Daniel A Horke and Adam S Chatterley and Alexandra Simperler and Helen H Fielding and Jan R R Verlet},

url = {http://xlink.rsc.org/?DOI=c2sc21737f},

doi = {10.1039/c2sc21737f},

year  = {2013},

date = {2013-01-01},

journal = {Chem. Sci.},

volume = {4},

number = {3},

pages = {921},

keywords = {Anion spectroscopy, dynamics, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:J.Phys.Chem.Lett.3:834,

title = {Femtosecond Photoelectron Imaging of Aligned Polyanions: Probing Molecular Dynamics through the Electron\textendashAnion Coulomb Repulsion},

author = {Daniel. A. Horke and Adam S. Chatterley and Jan R. R. Verlet},

url = {https://doi.org/10.1021/jz3000933},

doi = {10.1021/jz3000933},

issn = {1948-7185},

year  = {2012},

date = {2012-04-01},

urldate = {2019-04-03},

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

volume = {3},

number = {7},

pages = {834--838},

abstract = {The first time-resolved photoelectron imaging study of a polyanion is presented. Using the alignment induced through resonance excitation, the photoelectron angular distributions can be qualitatively understood in terms of the position of localized excess charges on the molecular skeleton, which influence the photoemission dynamics. Pump\textendash probe experiments are used to demonstrate that the photoelectron angular distribution is also sensitive to molecular dynamics. This is shown here for the rotational dynamics of a polyanion, in which the photoelectron anisotropy tracks the rotational coherence as it dephases. The methodology can in principle be applied to general molecular dynamics in large polyanions, providing a new route to studying ultrafast structural dynamics in complex gas-phase systems.},

keywords = {alignment, Anion spectroscopy, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Horke:Phys.Rev.Lett.108:083003,

title = {Effect of Internal Energy on the Repulsive Coulomb Barrier of Polyanions},

author = {Daniel A Horke and Adam S Chatterley and Jan R R Verlet},

url = {http://link.aps.org/doi/10.1103/PhysRevLett.108.083003},

doi = {10.1103/PhysRevLett.108.083003},

year  = {2012},

date = {2012-02-01},

journal = {Phys. Rev. Lett.},

volume = {108},

number = {8},

pages = {083003},

keywords = {photoelectron imaging, Photoelectron spectroscopy, polyanions, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}

@article{Chatterley:Phys.Chem.Chem.Phys.14:16155,

title = {On the Intrinsic Photophysics of Indigo: A Time-Resolved Photoelectron Spectroscopy Study of the Indigo Carmine Dianion},

author = {Adam S Chatterley and Daniel A Horke and Jan R R Verlet},

url = {http://xlink.rsc.org/?DOI=c2cp43275g},

doi = {10.1039/c2cp43275g},

year  = {2012},

date = {2012-01-01},

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

volume = {14},

number = {46},

pages = {16155},

keywords = {Anion spectroscopy, dynamics, Photoelectron spectroscopy, polyanions, velocity-map imaging},

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{Horke:Phys.Chem.Chem.Phys.13:19546,

title = {Time-Resolved Photoelectron Imaging of the Chloranil Radical Anion: Ultrafast Relaxation of Electronically Excited Electron Acceptor States},

author = {Daniel A Horke and Jan R R Verlet},

url = {http://xlink.rsc.org/?DOI=c1cp22237f},

doi = {10.1039/c1cp22237f},

year  = {2011},

date = {2011-01-01},

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

volume = {13},

number = {43},

pages = {19546--19552},

abstract = {The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion are investigated using photoelectron imaging. The photoelectron images taken at 480 nm clearly indicate resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. The ultrafast relaxation dynamics of excited states near threshold are pertinent to common electron acceptor molecules based on the quinone moiety and may serve as doorway states that enable efficient electron transfer in the highly exergonic inverted regime, despite the presence of large free energy barriers.},

keywords = {Anion spectroscopy, dynamics, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, 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}

}

@article{Roberts:Phys.Chem.Chem.Phys.12:6226,

title = {Spectroscopy and Dynamics of the 7,7,8,8-Tetracyanoquinodimethane Radical Anion.},

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

url = {http://dx.doi.org/10.1039/c001438a},

doi = {10.1039/c001438a},

year  = {2010},

date = {2010-01-01},

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

volume = {12},

number = {23},

pages = {6226--6232},

abstract = {The photoelectron spectrum of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion has been measured at 3.1 eV. Additionally, the ultrafast relaxation dynamics of the first excited state (1(2)B(3u)) of TCNQ(-) have been studied using time-resolved photoelectron spectroscopy, which reveals that it undergoes internal conversion back to the ground state ((2)B(2g)) with an associated lifetime of 650 fs and shows evidence of coherent nuclear motion. From Duplicate 1 ( Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethane radical anion. - Roberts, Gareth M; Lecointre, Julien; Horke, Daniel a; Verlet, Jan R R ) From Duplicate 1 ( Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethane radical anion. - Roberts, Gareth M; Lecointre, Julien; Horke, Daniel a; Verlet, Jan R R ) From Duplicate 1 ( Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethane radical anion. - Roberts, Gareth M; Lecointre, Julien; Horke, Daniel a; Verlet, Jan R R ) From Duplicate 1 ( Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethane radical anion. - Roberts, Gareth M; Lecointre, Julien; Horke, Daniel A; Verlet, Jan R R )},

keywords = {Anion spectroscopy, dynamics, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging},

pubstate = {published},

tppubtype = {article}

}