Peter J M van der Burgt | National University of Ireland, Maynooth (original) (raw)

Papers by Peter J M van der Burgt

Phys Chem Chem Phys, 2024

We have performed coincidence mass spectrometry of fragmentation of pyrene molecules by 70 eV ele... more We have performed coincidence mass spectrometry of fragmentation of pyrene molecules by 70 eV electron impact. Ionized fragments have been mass selected using a reflectron time-of-flight mass spectrometer, and a field programmable gate array has been used for the timing of the electron and ion extraction pulses and for the event-by-event detection of the ions. Double ionization results in a number of prominent fragmentations producing two singly-ionized fragments with kinetic energies of up to a few eV. A number of fragmentations produce ions with four or more carbon atoms, which can only be formed by the breaking of at least three CC bonds.

Europena Journal of Physics D, 2022

Double ionization of anthracene molecules by 70 eV electron impact results in a number of promine... more Double ionization of anthracene molecules by 70 eV electron impact results in a number of prominent fragmentations producing two singly ionized fragments. In our experiment, ionized fragments were detected using a reflectron time-of-flight mass spectrometer. A field programmable gate array was used for the timing and the recording of mass spectra on an event-by-event basis. A detailed model of the coincidence data acquisition was developed, enabling us to reliably obtain the map of true coincidences. Our measurements show that fragmentations for which the total number of carbon atoms in the two singly ionized fragments is even are generally significantly stronger than fragmentations for which the total is odd. No fragmentations are observed for a total number of 13 carbon atoms. There are only very weak fragmentations where one of the fragments only contains one carbon atom. Most of the fragments have 2 or 3 hydrogen atoms. There are several fragmentations in which the larger fragment has 9, 10, 11 or 12 carbon atoms and 5, 6, 7 or 8 hydrogen atoms. Fragments with only carbon atoms and no hydrogen atoms are not present, and only few fragmentations are observed with a fragment containing only one hydrogen atom.

The European Physical Journal D

Journal of Physics: Conference Series

We have measured sets of mass spectra for positive ions produced by low-energy electron impact on... more We have measured sets of mass spectra for positive ions produced by low-energy electron impact on phenanthrene. Ions have been mass resolved using a reflectron time-of-flight mass spectrometer, and the electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. The aim of this paper is to provide a detailed comparison of phenanthrene with its isomer anthracene, for which we have published results in a previous paper [1]. Appearance energies for a selection of fragment ions of phenanthrene have been determined, and are compared with anthracene. The most significant differences are observed in the ion yield curves of the ions containing 12 carbon atoms. The ion yield curves of phenanthrene have higher maximum yields and lower appearance energies compared to anthracene. For the fragments containing 9 and 10 carbon atoms the phenanthrene yields are slightly lower, but the appearance energies are the same as for anthracene. Small differences in yields are also observed for the fragments with 6 and 7 carbon atoms. The double and triple ionization energies of phenanthrene have been determined and are in agreement with anthracene.

The European Physical Journal D

We have measured mass spectra for positive ions produced by low-energy electron impact on anthrac... more We have measured mass spectra for positive ions produced by low-energy electron impact on anthracene using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. Appearance energies for all these ions have been determined, and we report the first direct measurement of the triple ionization energy of anthracene at 45.5 ± 0.5 eV. The groups of fragments containing 8-13 carbon atoms provide evidence for hydrogen rearrangements during the fragmentation, involving retention or loss of one or two additional hydrogen atoms. Groups of fragments with 6 and 7 carbon atoms clearly show the presence of doubly-charged fragments. The smaller fragments with 1-4 carbon atoms all show broadened peaks, and these fragments may be partly or mostly due to energetic charge-separation fragmentations of doubly-charged anthracene.

The European Physical Journal D

Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p 0 [1/2] 0 , 6p 0 [3/2]... more Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p 0 [1/2] 0 , 6p 0 [3/2] 2 , 7p[1/2] 0 , 7p[3/2] 2 , and 7p[5/2] 2 states of the Xe atom has been studied. Spectra of SE were recorded in the 800–3500 nm region, which covers the 6p 0 , 7p → 7s (2500–3500 nm), 6p 0 , 7p → 5d (1000–2000 nm), 7s → 6p (1200–1900 nm) transitions, as well as the near-IR 6p → 6s (800–1000 nm) transitions. It is shown that excitation of the 7p states results in radiative cascade via the 7s states, 7p → 7s → 6p, although at least one case of cascading via the 5d states is also observed. Spectra of SE induced by excitation of the 6p 0 states are dominated by the 6p 0 → 6s 0 transitions in the near IR and the 6p 0 → 5d[1/2] 1 → 6p[1/2] 1 → 6s[3/2] 1 cascade; the 6p 0 → 7s → 6p cascade is also observed, although the secondary 7s → 6p emission is rather weak in comparison with excitation of the 7p states.

We have measured mass spectra for positive ions produced by low-energy electron impact on cytosin... more We have measured mass spectra for positive ions produced by low-energy electron impact on cytosine using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. The ion yield curves have been normalized by comparing the sum of the ion yields to the average of calculated total ionization cross sections. Appearance energies of the fragment ions have been determined, showing that the fragments 68 u-84 u have appearance energies between 10 and 11 eV, whereas fragments of 55 u and lower mass all have appearance energies above 12 eV. Most of the ion yields of 55 u and smaller show multiple onsets. Several groups of fragments have ion yield curves with nearly the same shape, clearly indicating the relevance of tautomerization in the fragmentation of cytosine.

We define a model of physical devices that have a parallel atomic operation that transforms an un... more We define a model of physical devices that have a parallel atomic operation that transforms an unordered list input such that the sorted output can be sequentially read off in linear time. We show that commonly used biology, chemistry, and physics laboratory techniques are model instances and provide implementations.

We define a model of physical devices that have a parallel atomic operation that transforms an un... more We define a model of physical devices that have a parallel atomic operation that transforms an unordered list input such that the sorted output can be sequentially read off in linear time. We show that commonly used biology, chemistry, and physics laboratory techniques are model instances and provide implementations.

A new experiment has been set up for study of electron and photon impact fragmentation of cluster... more A new experiment has been set up for study of electron and photon impact fragmentation of clusters. Van der Waals clusters are generated in a supersonic expansion. The clusters are probed with energy-resolved electron impact and with photo-excitation and ionisation, and fragmentation into ions and long-lived neutral metastable species will be investigated. A reflectron time-of-flight mass spectrometer is used for mass-selective detection of ionized fragments. Time-of-flight detectors are used to measure kinetic energy distributions of neutral metastable fragments. Detection of neutral metastable fragments has been applied with great success in electron and photon impact dissociation of many different molecules, but has only recently been applied in fragmentation studies of rare-gas clusters. The intial focus will be on pure rare-gas clusters and metal-embedded rare-gas clusters (M·Rn clusters with M = Hg, Na, K, and R = Ar, Kr, Xe). An overview will be given of the apparatus, the data acquisition, and plans for the future.

The European Physical Journal D, 2015

Journal of Physics B Atomic and Molecular Physics

The authors have studied the near-threshold excitation of autoionising states in electron-helium ... more The authors have studied the near-threshold excitation of autoionising states in electron-helium scattering. Only a particular set of autoionising states is observed in the measurements, which has led them to formulate a selection rule for threshold excitation of autoionising states. Evidence is presented that autoionising states belonging to this particular set are strongly excited near their thresholds by hitherto unknown shape resonances.

Journal of Physics B Atomic and Molecular Physics

An optical potential method is used to formulate a model for the post-collision interaction that ... more An optical potential method is used to formulate a model for the post-collision interaction that occurs in electron-helium scattering after excitation and decay of autoionising states. The model is an extension of an earlier description given by Nienhuis and Heideman, and is used to study the effects of post-collision interaction in ejected-electron spectra. The authors present a calculation of angular distributions of ejected electrons from the He**(2s2)1S autoionising state. It is argued that study of angular momentum exchange during the post-collision interaction requires detailed knowledge of the interfering background of the direct ionisation process.

This paper discusses stimulated emission in the IR region induced by two-photon excitation of the... more This paper discusses stimulated emission in the IR region induced by two-photon excitation of the 6p'[1/2]0 , 6p'[3/2]2 ,7p[1/2]0 , 7p[3/2]2 and 7p[5/2]2 states of the Xe atom.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

This paper presents the results of an experimental investigation into collective effects in the t... more This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S(1/2) state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-alpha photons have been measured as a function of laser intensity (from 1 to 340 MW/cm(2)) and laser detuning around the 1S(1/2)-2S(1/2) two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S(1/2), 2P(1/2), and 2P(3/2) states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-alpha...

A new experiment has been set up for study of electron and photon impact fragmentation of cluster... more A new experiment has been set up for study of electron and photon impact fragmentation of clusters. Van der Waals clusters are generated in a supersonic expansion. The clusters are probed with energy-resolved electron impact and with photo-excitation and ionisation, and fragmentation into ions and long-lived neutral metastable species will be investigated. A reflectron time-of-flight mass spectrometer is used for

Journal of Physics B-atomic Molecular and Optical Physics, 1985

Four He- resonances with all three electrons in the n=2 shell are accessible by electron impact f... more Four He- resonances with all three electrons in the n=2 shell are accessible by electron impact from the He ground state but only two resonances have been identified unambiguously in electron-helium scattering experiments. Experimental evidence for the presence of a He- resonance at 59.90 eV in the excitation cross section of the He**(2s2p)3P autoionising state is presented and discussed.

Phys Chem Chem Phys, 2024

We have performed coincidence mass spectrometry of fragmentation of pyrene molecules by 70 eV ele... more We have performed coincidence mass spectrometry of fragmentation of pyrene molecules by 70 eV electron impact. Ionized fragments have been mass selected using a reflectron time-of-flight mass spectrometer, and a field programmable gate array has been used for the timing of the electron and ion extraction pulses and for the event-by-event detection of the ions. Double ionization results in a number of prominent fragmentations producing two singly-ionized fragments with kinetic energies of up to a few eV. A number of fragmentations produce ions with four or more carbon atoms, which can only be formed by the breaking of at least three CC bonds.

Europena Journal of Physics D, 2022

Double ionization of anthracene molecules by 70 eV electron impact results in a number of promine... more Double ionization of anthracene molecules by 70 eV electron impact results in a number of prominent fragmentations producing two singly ionized fragments. In our experiment, ionized fragments were detected using a reflectron time-of-flight mass spectrometer. A field programmable gate array was used for the timing and the recording of mass spectra on an event-by-event basis. A detailed model of the coincidence data acquisition was developed, enabling us to reliably obtain the map of true coincidences. Our measurements show that fragmentations for which the total number of carbon atoms in the two singly ionized fragments is even are generally significantly stronger than fragmentations for which the total is odd. No fragmentations are observed for a total number of 13 carbon atoms. There are only very weak fragmentations where one of the fragments only contains one carbon atom. Most of the fragments have 2 or 3 hydrogen atoms. There are several fragmentations in which the larger fragment has 9, 10, 11 or 12 carbon atoms and 5, 6, 7 or 8 hydrogen atoms. Fragments with only carbon atoms and no hydrogen atoms are not present, and only few fragmentations are observed with a fragment containing only one hydrogen atom.

The European Physical Journal D

Journal of Physics: Conference Series

We have measured sets of mass spectra for positive ions produced by low-energy electron impact on... more We have measured sets of mass spectra for positive ions produced by low-energy electron impact on phenanthrene. Ions have been mass resolved using a reflectron time-of-flight mass spectrometer, and the electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. The aim of this paper is to provide a detailed comparison of phenanthrene with its isomer anthracene, for which we have published results in a previous paper [1]. Appearance energies for a selection of fragment ions of phenanthrene have been determined, and are compared with anthracene. The most significant differences are observed in the ion yield curves of the ions containing 12 carbon atoms. The ion yield curves of phenanthrene have higher maximum yields and lower appearance energies compared to anthracene. For the fragments containing 9 and 10 carbon atoms the phenanthrene yields are slightly lower, but the appearance energies are the same as for anthracene. Small differences in yields are also observed for the fragments with 6 and 7 carbon atoms. The double and triple ionization energies of phenanthrene have been determined and are in agreement with anthracene.

The European Physical Journal D

We have measured mass spectra for positive ions produced by low-energy electron impact on anthrac... more We have measured mass spectra for positive ions produced by low-energy electron impact on anthracene using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. Appearance energies for all these ions have been determined, and we report the first direct measurement of the triple ionization energy of anthracene at 45.5 ± 0.5 eV. The groups of fragments containing 8-13 carbon atoms provide evidence for hydrogen rearrangements during the fragmentation, involving retention or loss of one or two additional hydrogen atoms. Groups of fragments with 6 and 7 carbon atoms clearly show the presence of doubly-charged fragments. The smaller fragments with 1-4 carbon atoms all show broadened peaks, and these fragments may be partly or mostly due to energetic charge-separation fragmentations of doubly-charged anthracene.

The European Physical Journal D

Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p 0 [1/2] 0 , 6p 0 [3/2]... more Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p 0 [1/2] 0 , 6p 0 [3/2] 2 , 7p[1/2] 0 , 7p[3/2] 2 , and 7p[5/2] 2 states of the Xe atom has been studied. Spectra of SE were recorded in the 800–3500 nm region, which covers the 6p 0 , 7p → 7s (2500–3500 nm), 6p 0 , 7p → 5d (1000–2000 nm), 7s → 6p (1200–1900 nm) transitions, as well as the near-IR 6p → 6s (800–1000 nm) transitions. It is shown that excitation of the 7p states results in radiative cascade via the 7s states, 7p → 7s → 6p, although at least one case of cascading via the 5d states is also observed. Spectra of SE induced by excitation of the 6p 0 states are dominated by the 6p 0 → 6s 0 transitions in the near IR and the 6p 0 → 5d[1/2] 1 → 6p[1/2] 1 → 6s[3/2] 1 cascade; the 6p 0 → 7s → 6p cascade is also observed, although the secondary 7s → 6p emission is rather weak in comparison with excitation of the 7p states.

We have measured mass spectra for positive ions produced by low-energy electron impact on cytosin... more We have measured mass spectra for positive ions produced by low-energy electron impact on cytosine using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. The ion yield curves have been normalized by comparing the sum of the ion yields to the average of calculated total ionization cross sections. Appearance energies of the fragment ions have been determined, showing that the fragments 68 u-84 u have appearance energies between 10 and 11 eV, whereas fragments of 55 u and lower mass all have appearance energies above 12 eV. Most of the ion yields of 55 u and smaller show multiple onsets. Several groups of fragments have ion yield curves with nearly the same shape, clearly indicating the relevance of tautomerization in the fragmentation of cytosine.

We define a model of physical devices that have a parallel atomic operation that transforms an un... more We define a model of physical devices that have a parallel atomic operation that transforms an unordered list input such that the sorted output can be sequentially read off in linear time. We show that commonly used biology, chemistry, and physics laboratory techniques are model instances and provide implementations.

We define a model of physical devices that have a parallel atomic operation that transforms an un... more We define a model of physical devices that have a parallel atomic operation that transforms an unordered list input such that the sorted output can be sequentially read off in linear time. We show that commonly used biology, chemistry, and physics laboratory techniques are model instances and provide implementations.

A new experiment has been set up for study of electron and photon impact fragmentation of cluster... more A new experiment has been set up for study of electron and photon impact fragmentation of clusters. Van der Waals clusters are generated in a supersonic expansion. The clusters are probed with energy-resolved electron impact and with photo-excitation and ionisation, and fragmentation into ions and long-lived neutral metastable species will be investigated. A reflectron time-of-flight mass spectrometer is used for mass-selective detection of ionized fragments. Time-of-flight detectors are used to measure kinetic energy distributions of neutral metastable fragments. Detection of neutral metastable fragments has been applied with great success in electron and photon impact dissociation of many different molecules, but has only recently been applied in fragmentation studies of rare-gas clusters. The intial focus will be on pure rare-gas clusters and metal-embedded rare-gas clusters (M·Rn clusters with M = Hg, Na, K, and R = Ar, Kr, Xe). An overview will be given of the apparatus, the data acquisition, and plans for the future.

The European Physical Journal D, 2015

Journal of Physics B Atomic and Molecular Physics

The authors have studied the near-threshold excitation of autoionising states in electron-helium ... more The authors have studied the near-threshold excitation of autoionising states in electron-helium scattering. Only a particular set of autoionising states is observed in the measurements, which has led them to formulate a selection rule for threshold excitation of autoionising states. Evidence is presented that autoionising states belonging to this particular set are strongly excited near their thresholds by hitherto unknown shape resonances.

Journal of Physics B Atomic and Molecular Physics

An optical potential method is used to formulate a model for the post-collision interaction that ... more An optical potential method is used to formulate a model for the post-collision interaction that occurs in electron-helium scattering after excitation and decay of autoionising states. The model is an extension of an earlier description given by Nienhuis and Heideman, and is used to study the effects of post-collision interaction in ejected-electron spectra. The authors present a calculation of angular distributions of ejected electrons from the He**(2s2)1S autoionising state. It is argued that study of angular momentum exchange during the post-collision interaction requires detailed knowledge of the interfering background of the direct ionisation process.

This paper discusses stimulated emission in the IR region induced by two-photon excitation of the... more This paper discusses stimulated emission in the IR region induced by two-photon excitation of the 6p'[1/2]0 , 6p'[3/2]2 ,7p[1/2]0 , 7p[3/2]2 and 7p[5/2]2 states of the Xe atom.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

This paper presents the results of an experimental investigation into collective effects in the t... more This paper presents the results of an experimental investigation into collective effects in the transient plasma formed by multiphoton ionization of atomic deuterium with a pulsed laser. The laser wavelength is varied in a narrow range around 243 nm, so that the photoionization is resonant with the metastable 2S(1/2) state. The ion yield, the ion time-of-flight spectra, and the yield of Lyman-alpha photons have been measured as a function of laser intensity (from 1 to 340 MW/cm(2)) and laser detuning around the 1S(1/2)-2S(1/2) two-photon resonance. During and shortly after the laser pulse, collective effects resulting from the mutual interaction of the photoelectrons and the ions affect the spatial and temporal distribution of the ions. Because of the near-degeneracy of the 2S(1/2), 2P(1/2), and 2P(3/2) states, the resonant multiphoton ionization is affected by the Stark mixing of these states in the collective field. As a result, the time-dependent yields of ions and of Lyman-alpha...

A new experiment has been set up for study of electron and photon impact fragmentation of cluster... more A new experiment has been set up for study of electron and photon impact fragmentation of clusters. Van der Waals clusters are generated in a supersonic expansion. The clusters are probed with energy-resolved electron impact and with photo-excitation and ionisation, and fragmentation into ions and long-lived neutral metastable species will be investigated. A reflectron time-of-flight mass spectrometer is used for

Journal of Physics B-atomic Molecular and Optical Physics, 1985

Four He- resonances with all three electrons in the n=2 shell are accessible by electron impact f... more Four He- resonances with all three electrons in the n=2 shell are accessible by electron impact from the He ground state but only two resonances have been identified unambiguously in electron-helium scattering experiments. Experimental evidence for the presence of a He- resonance at 59.90 eV in the excitation cross section of the He**(2s2p)3P autoionising state is presented and discussed.