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Recent Publications
Wang, Siwen; Dauletyarov, Yerbolat; Krüger, Peter; Horke, Daniel A.
High-throughput UV-photofragmentation studies of thymine and guanine Journal Article
In: Phys. Chem. Chem. Phys., vol. 25, pp. 12322, 2023.
@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 = {},
pubstate = {published},
tppubtype = {article}
}
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.
Caballo, Ana; Huits, Anders J. T. M.; Parker, David H.; Horke, Daniel 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.
@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 = {},
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.
Wang, Siwen; Abma, Grite L.; Krüger, Peter; Roij, Andre; Balster, Michiel; Janssen, Niek; Horke, Daniel A.
Comparing Pulsed and Continuous Laser-Induced Acoustic Desorption (LIAD) as Sources for Intact Biomolecules Journal Article
In: Eur. Phys. J. D, vol. 76, no. 7, pp. 128, 2022, ISSN: 1434-6060, 1434-6079.
@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 = {},
pubstate = {published},
tppubtype = {article}
}
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.