Here you will find all scientific publications from the group leader, Daniel Horke. Articles and materials written for a more general audience can be found on the Outreach pages. Recent posters from the group are in the gallery!
Filter Publications:
2023
6.
Caballo A, Huits A J T M, Parker D H, Horke D A
Disentangling Multiphoton Ionization and Dissociation Channels in Molecular Oxygen Using Photoelectron–Photoion Coincidence Imaging Journal Article
In: J. Phys. Chem. A, vol. 127, no. 1, pp. 92–98, 2023, ISSN: 1089-5639, 1520-5215.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging
@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}
}
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 $łeqsim$1 TW/cm2 to ensure excitation in the perturbative regime, where the possibility of resonance enhanced multiphoton ionization (REMPI) can be investigated. O2+ production is found to be resonance enhanced around 400 nm via three-photon excitation to the e$’$3$Delta$u(v = 0) state, similar to results from REMPI studies using nanosecond dye lasers. O+ production reaches 7% of the total ion yield around 405 nm due to two processes: autoionization following five-photon excitation of O2, producing O2+(X(v)) in a wide range of vibrational states followed by two- or three-photon dissociation, or six-photon excitation to a superexcited O2** state followed by neutral dissociation and subsequent ionization of the electronically excited O atom. Coincidence detection is shown to be crucial in identifying these competing pathways.
2021
5.
Caballo A, Huits A J T M, Vredenborg A, Balster M, Parker D H, Horke D A
Femtosecond 2 + 1 Resonance-Enhanced Multiphoton Ionization Spectroscopy of the C-State in Molecular Oxygen Journal Article
In: J. Phys. Chem. A, vol. 125, no. 41, pp. 9060–9064, 2021, ISSN: 1089-5639.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, Photoelectron spectroscopy, velocity-map imaging
@article{Caballo:J.Phys.Chem.A125:9060,
title = {Femtosecond 2 + 1 Resonance-Enhanced Multiphoton Ionization Spectroscopy of the C-State in Molecular Oxygen},
author = {Ana Caballo and Anders J. T. M. Huits and Arno Vredenborg and Michiel Balster and David H. Parker and Daniel A. Horke},
url = {https://doi.org/10.1021/acs.jpca.1c05541},
doi = {10.1021/acs.jpca.1c05541},
issn = {1089-5639},
year = {2021},
date = {2021-10-01},
journal = {J. Phys. Chem. A},
volume = {125},
number = {41},
pages = {9060--9064},
publisher = {American Chemical Society},
abstract = {Coincidence electron-cation imaging is used to characterize the multiphoton ionization of O2 via the v = 4,5 levels of the 3s(3$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$g(v = 5) level. A distinct 3s textrightarrow p wave character is observed in the photoelectron angular distribution for the v = 5 channel when on resonance.},
keywords = {Coincidence Imaging, Photoelectron spectroscopy, velocity-map imaging},
pubstate = {published},
tppubtype = {article}
}
Coincidence electron-cation imaging is used to characterize the multiphoton ionization of O2 via the v = 4,5 levels of the 3s(3$Pi$g) Rydberg state. A tunable 100 fs laser beam operating in the 271– 263 nm region is found to cause a nonresonant ionization across this wavelength range, with an additional resonant ionization channel only observed when tuned to the 3$Pi$g(v = 5) level. A distinct 3s textrightarrow p wave character is observed in the photoelectron angular distribution for the v = 5 channel when on resonance.
4.
Warne E M, Smith A D, Horke D A, Springate E, Jones A J H, Cacho C, Chapman R T, Minns R S
Time Resolved Detection of the S(1D) Product of the UV Induced Dissociation of CS2 Journal Article
In: J. Chem. Phys., vol. 154, no. 3, pp. 034302, 2021, ISSN: 0021-9606, 1089-7690.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, dynamics, HHG, Non-adiabatic dynamics, Photoelectron spectroscopy
@article{Warne:J.Chem.Phys.154:034302,
title = {Time Resolved Detection of the S(1D) Product of the UV Induced Dissociation of CS2},
author = {Emily M. Warne and Adam D. Smith and Daniel A. Horke and Emma Springate and Alfred J. H. Jones and Cephise Cacho and Richard T. Chapman and Russell S. Minns},
url = {http://aip.scitation.org/doi/10.1063/5.0035045},
doi = {10.1063/5.0035045},
issn = {0021-9606, 1089-7690},
year = {2021},
date = {2021-01-01},
urldate = {2021-06-21},
journal = {J. Chem. Phys.},
volume = {154},
number = {3},
pages = {034302},
abstract = {The products formed following the photodissociation of UV (200 nm) excited CS2 are monitored in a time resolved photoelectron spectroscopy experiment using femtosecond XUV (21.5 eV) photons. By spectrally resolving the electrons, we identify separate photoelectron bands related to the CS2 + h$nu$ textrightarrow S(1D) + CS and CS2 + h$nu$ textrightarrow S(3P) + CS dissociation channels, which show different appearance and rise times. The measurements show that there is no delay in the appearance of the S(1D) product contrary to the results of Horio et al. [J. Chem. Phys. 147, 013932 (2017)]. Analysis of the photoelectron yield associated with the atomic products allows us to obtain a S(3P)/S(1D) branching ratio and the rate constants associated with dissociation and intersystem crossing rather than the effective lifetime observed through the measurement of excited state populations alone.},
keywords = {Coincidence Imaging, dynamics, HHG, Non-adiabatic dynamics, Photoelectron spectroscopy},
pubstate = {published},
tppubtype = {article}
}
The products formed following the photodissociation of UV (200 nm) excited CS2 are monitored in a time resolved photoelectron spectroscopy experiment using femtosecond XUV (21.5 eV) photons. By spectrally resolving the electrons, we identify separate photoelectron bands related to the CS2 + h$nu$ textrightarrow S(1D) + CS and CS2 + h$nu$ textrightarrow S(3P) + CS dissociation channels, which show different appearance and rise times. The measurements show that there is no delay in the appearance of the S(1D) product contrary to the results of Horio et al. [J. Chem. Phys. 147, 013932 (2017)]. Analysis of the photoelectron yield associated with the atomic products allows us to obtain a S(3P)/S(1D) branching ratio and the rate constants associated with dissociation and intersystem crossing rather than the effective lifetime observed through the measurement of excited state populations alone.
2018
3.
Smith A D, Warne E M, Bellshaw D, Horke D A, Tudorovskya M, Springate E, Jones A J H, Cacho C, Chapman R T, Kirrander A, Minns R S
Mapping the Complete Reaction Path of a Complex Photochemical Reaction Journal Article
In: Phys. Rev. Lett., vol. 120, no. 18, pp. 183003, 2018.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, dynamics, HHG, Non-adiabatic dynamics, Photoelectron spectroscopy
@article{Smith:Phys.Rev.Lett.120:183003,
title = {Mapping the Complete Reaction Path of a Complex Photochemical Reaction},
author = {Adam D. Smith and Emily M. Warne and Darren Bellshaw and Daniel A. Horke and Maria Tudorovskya and Emma Springate and Alfred J. H. Jones and Cephise Cacho and Richard T. Chapman and Adam Kirrander and Russell S. Minns},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.183003},
doi = {10.1103/PhysRevLett.120.183003},
year = {2018},
date = {2018-05-01},
urldate = {2019-01-24},
journal = {Phys. Rev. Lett.},
volume = {120},
number = {18},
pages = {183003},
abstract = {We probe the dynamics of dissociating CS2 molecules across the entire reaction pathway upon excitation. Photoelectron spectroscopy measurements using laboratory-generated femtosecond extreme ultraviolet pulses monitor the competing dissociation, internal conversion, and intersystem crossing dynamics. Dissociation occurs either in the initially excited singlet manifold or, via intersystem crossing, in the triplet manifold. Both product channels are monitored and show that, despite being more rapid, the singlet dissociation is the minor product and that triplet state products dominate the final yield. We explain this by a consideration of accurate potential energy curves for both the singlet and triplet states. We propose that rapid internal conversion stabilizes the singlet population dynamically, allowing for singlet-triplet relaxation via intersystem crossing and the efficient formation of spin-forbidden dissociation products on longer timescales. The study demonstrates the importance of measuring the full reaction pathway for defining accurate reaction mechanisms.},
keywords = {Coincidence Imaging, dynamics, HHG, Non-adiabatic dynamics, Photoelectron spectroscopy},
pubstate = {published},
tppubtype = {article}
}
We probe the dynamics of dissociating CS2 molecules across the entire reaction pathway upon excitation. Photoelectron spectroscopy measurements using laboratory-generated femtosecond extreme ultraviolet pulses monitor the competing dissociation, internal conversion, and intersystem crossing dynamics. Dissociation occurs either in the initially excited singlet manifold or, via intersystem crossing, in the triplet manifold. Both product channels are monitored and show that, despite being more rapid, the singlet dissociation is the minor product and that triplet state products dominate the final yield. We explain this by a consideration of accurate potential energy curves for both the singlet and triplet states. We propose that rapid internal conversion stabilizes the singlet population dynamically, allowing for singlet-triplet relaxation via intersystem crossing and the efficient formation of spin-forbidden dissociation products on longer timescales. The study demonstrates the importance of measuring the full reaction pathway for defining accurate reaction mechanisms.
2016
2.
Horke D A, Watts H M, Smith A D, Jager E, Springate E, Alexander O, Cacho C, Chapman R T, Minns R S
Hydrogen Bonds in Excited State Proton Transfer Journal Article
In: Phys. Rev. Lett., vol. 117, no. 16, pp. 163002, 2016.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, intramolecular interactions, Isomer-effects, Non-adiabatic dynamics, photoelectron imaging, Photoelectron spectroscopy, velocity-map imaging
@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}
}
Hydrogen bonding may safeguard biomolecules against the damaging effects of UV light.
1.
Rothhardt J, Hädrich S, Shamir Y, Tschnernajew M, Klas R, Hoffmann A, Tadesse G K, Klenke A, Gottschall T, Eidam T, Limpert J, Tünnermann A, Boll R, Bomme C, Dachraoui H, Erk B, Fraia M D, Horke D A, Kierspel T, Mullins T, Przystawik A, Savelyev E, Wiese J, Laarmann T, Küpper J, Rolles D
High-Repetition-Rate and High-Photon-Flux 70 eV High-Harmonic Source for Coincidence Ion Imaging of Gas-Phase Molecules Journal Article
In: Optics Express, vol. 24, no. 16, pp. 18133–18147, 2016.
Abstract | Links | BibTeX | Altmetric | Tags: Coincidence Imaging, HHG, velocity-map imaging
@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}
}
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.