ORCID Profile
0000-0002-4621-4552
Current Organisation
Lawrence Berkely National Laboratory
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Publisher: IOP Publishing
Date: 11-2009
Publisher: AIP Publishing
Date: 11-01-2023
DOI: 10.1063/5.0128846
Abstract: We present an experimental and theoretical energy- and angle-resolved investigation on the non-dissociative photoionization dynamics of near-resonant, one-color, two-photon, single valence ionization of neutral O2 molecules. Using 9.3 eV femtosecond pulses produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and O2+ cations produced from one-color, two-photon ionization in coincidence. The measured and calculated photoelectron angular distributions show agreement, which indicates that a superposition of two intermediate electronic states is dominantly involved and that wavepacket motion on those near-resonantly populated intermediate states does not play a significant role in the measured two-photon ionization dynamics. Here, we find greater utility in the diabatic representation compared to the adiabatic representation, where invoking a single valence-character diabat is sufficient to describe the underlying two-photon ionization mechanism.
Publisher: American Physical Society (APS)
Date: 16-07-2018
Publisher: IOP Publishing
Date: 04-2009
Publisher: Springer Science and Business Media LLC
Date: 10-2022
Publisher: American Physical Society (APS)
Date: 03-03-2011
Publisher: IOP Publishing
Date: 11-2009
Publisher: IOP Publishing
Date: 2020
DOI: 10.1088/1742-6596/1412/15/152019
Abstract: We have conducted an experimental study on the photo double ionization (PDI) of carbon dioxide dimers and oxygen dimers, while focusing on the dissociation dynamics upon single photon absorption. The results in terms of the kinetic energy and angular distributions of the charged particles show unambiguous experimental evidence of intermolecular Coulombic decay (ICD) in carbon dioxide dimers. In the oxygen dimer, the results show that ICD is accompanied by knock-off ionization mechanisms.
Publisher: American Physical Society (APS)
Date: 28-05-2013
Publisher: IOP Publishing
Date: 2020
DOI: 10.1088/1742-6596/1412/7/072048
Abstract: New experimental results are presented on the dissociation dynamics of small neutral molecules in time-resolved photoexcitation-photoionization experiments by ultrashort vacuum- and extreme-ultraviolet laser pulses and charged particle momentum imaging.
Publisher: American Physical Society (APS)
Date: 09-10-2020
Publisher: OSA
Date: 2014
Publisher: IOP Publishing
Date: 05-11-2012
Publisher: IOP Publishing
Date: 05-11-2012
Publisher: OSA
Date: 2013
Publisher: IOP Publishing
Date: 17-04-2015
Publisher: American Physical Society (APS)
Date: 27-01-2021
Publisher: AIP Publishing
Date: 19-10-2018
DOI: 10.1063/1.5046521
Abstract: New photoresists are needed to advance extreme ultraviolet (EUV) lithography. The tailored design of efficient photoresists is enabled by a fundamental understanding of EUV induced chemistry. Processes that occur in the resist film after absorption of an EUV photon are discussed, and a new approach to study these processes on a fundamental level is described. The processes of photoabsorption, electron emission, and molecular fragmentation were studied experimentally in the gas-phase on analogs of the monomer units employed in chemically lified EUV resists. To demonstrate the dependence of the EUV absorption cross section on selective light harvesting substituents, halogenated methylphenols were characterized employing the following techniques. Photoelectron spectroscopy was utilized to investigate kinetic energies and yield of electrons emitted by a molecule. The emission of Auger electrons was detected following photoionization in the case of iodo-methylphenol. Mass-spectrometry was used to deduce the molecular fragmentation pathways following electron emission and atomic relaxation. To gain insight on the interaction of emitted electrons with neutral molecules in a condensed film, the fragmentation pattern of neutral gas-phase molecules, interacting with an electron beam, was studied and observed to be similar to EUV photon fragmentation. Below the ionization threshold, electrons were confirmed to dissociate iodo-methylphenol by resonant electron attachment.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0CP01522A
Abstract: 3D momentum imaging investigation of the dynamics of dissociative electron attachment to formic acid, producing a hydride anion and either formyloxyl or hydrocarboxyl radicals.
Publisher: IOP Publishing
Date: 11-2009
Publisher: SPIE
Date: 03-09-2018
DOI: 10.1117/12.2321323
Publisher: American Physical Society (APS)
Date: 30-08-2013
Publisher: SPIE
Date: 16-10-2017
DOI: 10.1117/12.2281520
Publisher: American Physical Society (APS)
Date: 07-12-2009
Publisher: American Physical Society (APS)
Date: 22-09-2009
Publisher: The Optical Society
Date: 29-07-2016
DOI: 10.1364/OE.24.018209
Publisher: IOP Publishing
Date: 19-11-2020
Abstract: We present state-selective measurements on the N H 2 + + H + and NH + + H + + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH 3 , where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the N H 2 + + H + dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold N H 2 + fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited N H 2 + fragment with roughly 1 eV of internal energy. The NH + + H + + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the N H 2 + + H + channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states.
Publisher: IOP Publishing
Date: 2020
DOI: 10.1088/1742-6596/1412/5/052004
Abstract: We report recent results of mass-resolved anion fragment momentum imaging experiments to investigate dissociative electron attachment to formic acid, for incident energies between 5 eV and 9 eV. A remarkable site-selectivity is found for a resonance at 8.5 eV by comparing anion fragment yields for two deuterated isotopologues of formic acid. This results in an H − fragment from the O-H bond of the transient anion, with negligible contribution from C-H break. In contrast, a lower-energy resonance at 7.1 eV dissociates by C–H or O–H break to produce H − and the neutral radicals HOCO or HCOO.
Publisher: IOP Publishing
Date: 23-09-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CP03637C
Abstract: Photoionization of the 4t 2 orbital of CF 4 shows overlapping resonances close to threshold, leading to a striking inversion of the photoelectron angular distribution when viewed in the body-frame.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP04178C
Abstract: We show that a single T 2 resonance can explain the 10 eV dissociative electron attachment peak in methane.
Publisher: Springer Science and Business Media LLC
Date: 09-2022
DOI: 10.1038/S41467-022-32836-6
Abstract: The double photoionization of a molecule by one photon ejects two electrons and typically creates an unstable dication. Observing the subsequent fragmentation products in coincidence can reveal a surprisingly detailed picture of the dynamics. Determining the time evolution and quantum mechanical states involved leads to deeper understanding of molecular dynamics. Here in a combined experimental and theoretical study, we unambiguously separate the sequential breakup via D + + OD + intermediates, from other processes leading to the same D + + D + + O final products of double ionization of water by a single photon. Moreover, we experimentally identify, separate, and follow step by step, two pathways involving the b 1 Σ + and a 1 Δ electronic states of the intermediate OD + ion. Our classical trajectory calculations on the relevant potential energy surfaces reproduce well the measured data and, combined with the experiment, enable the determination of the internal energy and angular momentum distribution of the OD + intermediate.
Publisher: IOP Publishing
Date: 17-01-2011
Publisher: American Physical Society (APS)
Date: 03-12-2019
Publisher: IOP Publishing
Date: 11-2009
Publisher: IOP Publishing
Date: 11-2009
Publisher: American Physical Society (APS)
Date: 11-09-2013
Publisher: AIP Publishing
Date: 06-2016
DOI: 10.1063/1.4953441
Abstract: We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.
Publisher: AIP Publishing
Date: 14-07-2020
DOI: 10.1063/5.0013485
Abstract: We present a combined experimental and theoretical study on the photodissociation dynamics of ion-pair formation in O2 following resonant two-photon absorption of a 9.3 eV femtosecond pulse, where the resulting O+ ions are detected using 3D momentum imaging. Ion-pair formation states of Σg−3 and 3Πg symmetry are accessed through predissociation of optically dark continuum Rydberg states converging to the B Σg−2 ionic state, which are resonantly populated via a mixture of both parallel–parallel and parallel–perpendicular two-photon transitions. This mixture is evident in the angular distribution of the dissociation relative to the light polarization and varies with the kinetic energy release (KER) of the fragmenting ion pair. The KER-dependent photoion angular distribution reveals the underlying two-photon absorption dynamics involved in the ion-pair production mechanism and indicates the existence of two nearly degenerate continuum resonances possessing different symmetries, which can decay by coupling to ion-pair states of the same total symmetry through internal conversion.
Publisher: American Chemical Society (ACS)
Date: 07-09-2022
Publisher: American Physical Society (APS)
Date: 08-09-2011
Publisher: AIP Publishing
Date: 02-2012
DOI: 10.1063/1.3685244
Abstract: We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H− from H2O− (2B1) and O− from \\documentclass[12pt]{minimal}\\begin{document}${\\rm O}_2^-$\\end{document}O2− (2Πu). The results are compared with existing experimental and theoretical data.
Publisher: MDPI AG
Date: 29-07-2023
Abstract: In this study, we present a complete set of electron scattering cross-sections from 1-Methyl-5-Nitroimidazole (1M5NI) molecules for impact energies ranging from 0.1 to 1000 eV. This information is relevant to evaluate the potential role of 1M5NI as a molecular radiosensitizers. The total electron scattering cross-sections (TCS) that we previously measured with a magnetically confined electron transmission apparatus were considered as the reference values for the present analysis. Elastic scattering cross-sections were calculated by means of two different schemes: The Schwinger multichannel (SMC) method for the lower energies (below 15 eV) and the independent atom model-based screening-corrected additivity rule with interferences (IAM-SCARI) for higher energies (above 15 eV). The latter was also applied to calculate the total ionization cross-sections, which were complemented with experimental values of the induced cationic fragmentation by electron impact. Double differential ionization cross-sections were measured with a reaction microscope multi-particle coincidence spectrometer. Using a momentum imaging spectrometer, direct measurements of the anion fragment yields and kinetic energies by the dissociative electron attachment are also presented. Cross-sections for the other inelastic channels were derived with a self-consistent procedure by s ling their values at a given energy to ensure that the sum of the cross-sections of all the scattering processes available at that energy coincides with the corresponding TCS. This cross-section data set is ready to be used for modelling electron-induced radiation damage at the molecular level to biologically relevant media containing 1M5NI as a potential radiosensitizer. Nonetheless, a proper evaluation of its radiosensitizing effects would require further radiobiological experiments.
Publisher: American Physical Society (APS)
Date: 29-06-2007
Publisher: IOP Publishing
Date: 20-09-2021
Publisher: AIP Publishing
Date: 15-03-2019
DOI: 10.1063/1.5079549
Abstract: The electronic and nuclear dynamics in methanol, following 156 nm photoexcitation, are investigated by combining a detailed analysis of time-resolved photoelectron spectroscopy experiments with electronic structure calculations. The photoexcitation pump pulse is followed by a delayed 260 nm photoionization probe pulse to produce photoelectrons that are analyzed by velocity map imaging. The yields of mass-resolved ions, measured with similar experimental conditions, are found to exhibit the same time-dependence as specific photoelectron spectral features. Energy-resolved signal onset and decay times are extracted from the measured photoelectron spectra to achieve high temporal resolution, beyond the 20 fs pump and probe pulse durations. When combined with ab initio calculations of selected cuts through the excited state potential energy surfaces, this information allows the dynamics of the transient excited molecule, which exhibits multiple nuclear and electronic degrees of freedom, to be tracked on its intrinsic few-femtosecond time scale. Within 15 fs of photoexcitation, we observe nuclear motion on the initially bound photoexcited 21A″ (S2) electronic state, through a conical intersection with the 11A′ (S3) state, which reveals paths to photodissociation following C–O stretch and C–O–H angle opening.
Publisher: IOP Publishing
Date: 10-2008
Publisher: Springer International Publishing
Date: 2015
Publisher: AIP Publishing
Date: 05-2020
DOI: 10.1063/1.5144482
Abstract: We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the 3rd-order nonlinear optical susceptibility. A non-collinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect. Optical homodyne and optical heterodyne detections are demonstrated to measure the 3rd-order nonlinear optical response for the S1 excited state of liquid nitrobenzene, which is populated by 2-photon absorption of a 780 nm 40 fs excitation pulse.
Publisher: American Chemical Society (ACS)
Date: 27-09-2019
Publisher: American Physical Society (APS)
Date: 05-06-2020
Publisher: American Chemical Society (ACS)
Date: 08-03-2020
Publisher: IOP Publishing
Date: 21-10-2009
Publisher: IOP Publishing
Date: 07-09-2015
Publisher: American Physical Society (APS)
Date: 26-08-2021
Publisher: SPIE
Date: 25-03-2019
DOI: 10.1117/12.2515134
Publisher: AIP Publishing
Date: 09-2023
DOI: 10.1063/5.0148194
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3CP02438E
Abstract: Creation of a super-excited radical water cation results in a long-lived excited oxygen fragment that can act as a destructive carrier and initiate secondary reactions such as breakup of DNA strands – a key radiation damage mechanism.
Publisher: IOP Publishing
Date: 05-11-2012
Publisher: American Physical Society (APS)
Date: 12-05-2016
Publisher: IOP Publishing
Date: 25-10-2016
Publisher: American Physical Society (APS)
Date: 15-04-2019
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4FD00036F
Abstract: Time-resolved core-level spectroscopy using laser pulses to initiate and short X-ray pulses to trace photoinduced processes has the unique potential to provide electronic state- and atomic site-specific insight into fundamental electron dynamics in complex systems. Time-domain studies using transient X-ray absorption and emission techniques have proven extremely valuable to investigate electronic and structural dynamics in isolated and solvated molecules. Here, we describe the implementation of a picosecond time-resolved X-ray photoelectron spectroscopy (TRXPS) technique at the Advanced Light Source (ALS) and its application to monitor photoinduced electron dynamics at the technologically pertinent interface formed by N3 dye molecules anchored to nanoporous ZnO. Indications for a dynamical chemical shift of the Ru3d photoemission line originating from the N3 metal centre are observed ∼30 ps after resonant HOMO–LUMO excitation with a visible laser pump pulse. The transient changes in the TRXPS spectra are accompanied by a characteristic surface photovoltage (SPV) response of the ZnO substrate on a pico- to nanosecond time scale. The interplay between the two phenomena is discussed in the context of possible electronic relaxation and recombination pathways that lead to the neutralisation of the transiently oxidised dye after ultrafast electron injection. A detailed account of the experimental technique is given including an analysis of the chemical modification of the nano-structured ZnO substrate during extended periods of solution-based dye sensitisation and its relevance for studies using surface-sensitive spectroscopy techniques.
Publisher: AIP Publishing
Date: 05-09-2023
DOI: 10.1063/5.0159300
Publisher: American Physical Society (APS)
Date: 13-08-2010
Publisher: American Physical Society (APS)
Date: 11-08-2020
Publisher: AIP
Date: 2006
DOI: 10.1063/1.2165640
Publisher: Springer Science and Business Media LLC
Date: 16-10-2017
DOI: 10.1038/NPHYS4308
Publisher: American Chemical Society (ACS)
Date: 23-10-2014
DOI: 10.1021/JZ501907D
Abstract: We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.
Publisher: American Physical Society (APS)
Date: 23-12-2020
Location: United States of America
No related grants have been discovered for Daniel Slaughter.