In our group we push the boundaries of how we can study molecules in the gas-phase. We develop novel methods to transfer ever large and more fragile (neutral) systems into the gas-phase, as well as new ways to control and probe these molecules. This development of these new methodologies is driven by scientific curiosity, but also real-world applications such as new analytical techniques.
You can also find some recent posters from the group in the gallery!
Structural-isomer effects in photochemistry
We know that in nature small structural changes – the rotation around a single bond or the relocation of a hydrogen atom – can significantly alter chemical functionality. But actually studying the structure-function relationship on this level is very challenging, as it is often impossible to separate these distinguish these different molecular structures. Yet this is exactly what we aim to do in this project by combining the electrostatic deflection technique with time-resolved spectroscopic methods. The electrostatic deflector allow us to select a single structural isomer (such as a conformer or tautomer) on the basis of its dipole moment. The isomer-selected samples can then be probes used methods that are not inherently isomer-sensitive themselves, such as ultrafast time-resolved photoelectron imaging experiments. This combination allows us to investigate how small structural changes, such as isomerism, influence the underlying photochemistry and chemical functionality.
@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 = {},
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 = {},
pubstate = {published},
tppubtype = {article}
}
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.
@article{Teschmit:Angew.Chem.Int.Ed.57:13775,
title = {Spatially Separating the Conformers of a Dipeptide},
author = {Nicole Teschmit and Daniel A. Horke and Jochen K\"{u}pper},
url = {https://onlinelibrary.wiley.com/doi/full/10.1002/anie.201807646},
doi = {10.1002/anie.201807646},
year = {2018},
date = {2018-08-01},
journal = {Angew. Chem. Int. Ed.},
volume = {57},
pages = {13775--13779},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Detecting chiral molecules with photoelectron circular dichroism
Chiral molecules, that is molecules with non-superimposable mirror images, are of crucial importance in pharmaceutical, agricultural and chemical industries. Yet the reliable and fast quantisation of chirality, and measurement of the enantiomeric excess, are non trivial. One promising new approach to detect chirality is imaging the photoelectrons produced following ionisation of a molecule by circular-polarised light (photoelectron circular dichroism – PECD). This approach has been shown to have orders of magnitude higher chiral responses than established analytical approaches.
As part of a consortium of partners from both academia and industry we are working on developing photoelectron circular dichroism (PECD) spectroscopy as an analytical tool. In particular we work closely together with the start-up MassSpecpecD on the development of a compact PECD-spectrometer for analytical applications.
Novel analytical tools for biomolecules
We are developing novel tools to analyse and study biologically relevant molecules (and other fragile systems) in the gas-phase. In particular we are developing soft vaporisation methods, that allows the intact transfer of large, fragile or non-volatile species into the gas-phase. Here we can study them using state-of-the-art spectroscopic or mass spectrometry techniques.
In particular we are working on a new approach termed laser-based thermal desorption (LBTD) that allows us to transfer fragile molecules from dilute solutions into the gas-phase, via deposition onto a thin inert metal foil. We have recently shown that this even allows us to transfer dipeptides or lipids intact in the spectrometer chamber, and at high densities.
@article{molecules28135058,
title = {High-Throughput UV Photoionization and Fragmentation of Neutral Biomolecules as a Structural Fingerprint},
author = {Siwen Wang and Yerbolat Dauletyarov and Daniel A. Horke},
doi = {10.3390/molecules28135058},
issn = {1420-3049},
year = {2023},
date = {2023-06-28},
urldate = {2023-06-28},
journal = {Molecules},
volume = {28},
number = {13},
pages = {5058},
abstract = {We present UV photofragmentation studies of the structural isomers paracetamol, 3-Pyridinepropionic acid (3-PPIA) and (R)-(-)-2-Phenylglycine. In particular, we utilized a new laser-based thermal desorption source in combination with femtosecond multiphoton ionization at 343 nm and 257 nm. The continuous nature of our molecule source, combined with the 50 kHz repetition rate of the laser, allowed us to perform these experiments at high throughput. In particular, we present detailed laser intensity dependence studies at both wavelengths, producing 2D mass spectra with highly differential information about the underlying fragmentation processes. We show that UV photofragmentation produces highly isomer-specific mass spectra, and assign all major fragmentation pathways observed. The intensity-dependence measurements, furthermore, allowed us to evaluate the appearance intensities for each fragmentation channel, which helped to distinguish competing from consecutive fragmentation pathways.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present UV photofragmentation studies of the structural isomers paracetamol, 3-Pyridinepropionic acid (3-PPIA) and (R)-(-)-2-Phenylglycine. In particular, we utilized a new laser-based thermal desorption source in combination with femtosecond multiphoton ionization at 343 nm and 257 nm. The continuous nature of our molecule source, combined with the 50 kHz repetition rate of the laser, allowed us to perform these experiments at high throughput. In particular, we present detailed laser intensity dependence studies at both wavelengths, producing 2D mass spectra with highly differential information about the underlying fragmentation processes. We show that UV photofragmentation produces highly isomer-specific mass spectra, and assign all major fragmentation pathways observed. The intensity-dependence measurements, furthermore, allowed us to evaluate the appearance intensities for each fragmentation channel, which helped to distinguish competing from consecutive fragmentation pathways.
@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 = {},
pubstate = {published},
tppubtype = {article}
}
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.
@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.
@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 = {},
pubstate = {published},
tppubtype = {article}
}
Recent advances in optical technologies now offer unprecedented opportunities for producing coherent and short-pulsed light (lasers) also at high photon energies, such as in the XUV (extreme ultraviolet) and even x-ray spectral regions. These allow us to explore new ways of performing time-resolved spectroscopies. In particular in combination with methods based on photoionization, such as photoelectron spectroscopy, this enables the realization of so-called universal probes, that can follow a photochemical process from reactants, through intermediates, to final products in real-time.
In collaboration with the group of Russell Minns (Southampton, UK) and the Artemis facility (STFC, Rutherford-Appleton lab) we are working on using XUV radiation produced through high-harmonic generation as a probe for photochemical processes.
Recent publications:
Abma, Grite L.; Parkes, Michael A.; Razmus, Weronika O.; Zhang, Yu; Wyatt, Adam S.; Springate, Emma; Chapman, Richard T.; Horke, Daniel A.; Minns, Russell S.: Direct Observation of a Roaming Intermediate and Its Dynamics. In: J. Am. Chem. Soc., vol. 146, no. 18, pp. 12595-12600, 2024.(Type: Journal Article | Links | BibTeX | Altmetric)
@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 = {},
pubstate = {published},
tppubtype = {article}
}
@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 = {},
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.
@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 = {},
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.
Studying the dynamics of photon-driven processes (i.e. photochemistry!) is now a well established method. However, there is more to chemistry than photon-driven processes and reactions. In this new project we aim to ‘transfer’ many of the techniques we have developed to study photon-driven processes towards studying electron-driven processes (i.e. electrochemistry!). We aim to establish time-resolved electron-pump photon-probe spectroscopy to directly follow chemical processes initiated by electrons. In particular, we are interested in (dissociative) electron attachment reactions. These are at the heart of many biological damage processes, both detrimental (ionising radiation that destroys DNA) and beneficial (radiation therapy as a cancer treatment).
Ana’s new paper combining coincidence imaging with femtosecond REMPI spectroscopy in oxygen is now online in JPCA – https://doi.org/10.1021/acs.jpca.1c05541
