Showing papers on "Ionization published in 2019"
TL;DR: The authors show the double-slit interference effect in the strong-field ionization of neon dimers by employing COLTRIMS method to record the momentum distribution of the photoelectrons in the molecular frame.
Abstract: Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. Here, we report on the observation of two-center interference in the molecular-frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which are measured in coincidence with electrons, allows choosing the symmetry of the residual ion, leading to observation of both, gerade and ungerade, types of interference.
7,160 citations
Columbia University1, Stockholm University2, University of Bologna3, University of Mainz4, University of Münster5, University of Coimbra6, University of Turin7, New York University Abu Dhabi8, University of Zurich9, Rensselaer Polytechnic Institute10, University of Amsterdam11, Max Planck Society12, Weizmann Institute of Science13, University of Freiburg14, University of Nantes15, Purdue University16, University of California, San Diego17, University of Chicago18, Nagoya University19, Pierre-and-Marie-Curie University20, Université Paris-Saclay21, Rice University22, University of California, Los Angeles23
TL;DR: Constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment are reported, and no DM or CEvNS detection may be claimed because the authors cannot model all of their backgrounds.
Abstract: We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation signal, leaving an effective exposure of (22±3) tonne day. Above ∼0.4 keVee, we observe 30 MeV/c2, and absorption of dark photons and axionlike particles for mχ within 0.186–1 keV/c2.
412 citations
TL;DR: It is established that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy and it is shown that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%.
Abstract: Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.
190 citations
Columbia University1, Stockholm University2, University of Bologna3, University of Mainz4, University of Münster5, University of Coimbra6, University of Turin7, New York University Abu Dhabi8, University of Zurich9, Rensselaer Polytechnic Institute10, University of Amsterdam11, Max Planck Society12, Weizmann Institute of Science13, University of Freiburg14, University of Nantes15, Purdue University16, University of California, San Diego17, University of Chicago18, Nagoya University19, Pierre-and-Marie-Curie University20, Université Paris-Saclay21, Rice University22, University of California, Los Angeles23
TL;DR: A probe of low-mass dark matter with masses down to about 85 MeV/c^{2} is reported on by looking for electronic recoils induced by the Migdal effect and bremsstrahlung using data from the XENON1T experiment, and exploiting an approach that uses ionization signals only allows for a lower detection threshold.
Abstract: Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above ∼5 GeV/c2, but have limited sensitivity to lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a bremsstrahlung photon. In this Letter, we report on a probe of low-mass dark matter with masses down to about 85 MeV/c2 by looking for electronic recoils induced by the Migdal effect and bremsstrahlung using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.
184 citations
TL;DR: In this article, the Coulomb potential was identified as the sole cause of the measured angle between the directions of electron emission and peak electric field, and an upper limit of 1.8 attoseconds on any tunnelling delay was established.
Abstract: The tunnelling of a particle through a potential barrier is a key feature of quantum mechanics that goes to the core of wave–particle duality. The phenomenon has no counterpart in classical physics, and there are no well constructed dynamical observables that could be used to determine ‘tunnelling times’. The resulting debate1–5 about whether a tunnelling quantum particle spends a finite and measurable time under a potential barrier was reignited in recent years by the advent of ultrafast lasers and attosecond metrology6. Particularly important is the attosecond angular streaking (‘attoclock’) technique7, which can time the release of electrons in strong-field ionization with a precision of a few attoseconds. Initial measurements7–10 confirmed the prevailing view that tunnelling is instantaneous, but later studies11,12 involving multi-electron atoms—which cannot be accurately modelled, complicating interpretation of the ionization dynamics—claimed evidence for finite tunnelling times. By contrast, the simplicity of the hydrogen atom enables precise experimental measurements and calculations13–15 and makes it a convenient benchmark. Here we report attoclock and momentum-space imaging16 experiments on atomic hydrogen and compare these results with accurate simulations based on the three-dimensional time-dependent Schrodinger equation and our experimental laser pulse parameters. We find excellent agreement between measured and simulated data, confirming the conclusions of an earlier theoretical study17 of the attoclock technique in atomic hydrogen that presented a compelling argument for instantaneous tunnelling. In addition, we identify the Coulomb potential as the sole cause of the measured angle between the directions of electron emission and peak electric field: this angle had been attributed11,12 to finite tunnelling times. We put an upper limit of 1.8 attoseconds on any tunnelling delay, in agreement with recent theoretical findings18 and ruling out the interpretation of all commonly used ‘tunnelling times’19 as ‘time spent by an electron under the potential barrier’20. Simulation and measurement of the photoionization of atomic hydrogen at attosecond resolution confirm that the tunnelling of the ejected electron is instantaneous.
168 citations
TL;DR: In this paper, the authors used ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium (KRb) molecules at a temperature of 500 nanokelvin.
Abstract: Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. In this study, we took the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest rovibronic quantum state at ultralow temperatures, thereby markedly reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium (KRb) molecules at a temperature of 500 nanokelvin, we directly observed reactants, intermediates, and products of the reaction 40K87Rb + 40K87Rb → K2Rb2* → K2 + Rb2. Beyond observation of a long-lived, energy-rich intermediate complex, this technique opens the door to further studies of quantum-state–resolved reaction dynamics in the ultracold regime.
163 citations
TL;DR: A fully analytical implementation of the core-valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states, yielding similar spectral profiles but with absolute core excitation and ionization energies that are systematically closer to the corresponding experimental data.
Abstract: We present a fully analytical implementation of the core–valence separation (CVS) scheme for the equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method for calculations of core-level states. Inspired by the CVS idea as originally formulated by Cederbaum, Domcke, and Schirmer, pure valence excitations are excluded from the EOM target space and the frozen-core approximation is imposed on the reference-state amplitudes and multipliers. This yields an efficient, robust, practical, and numerically balanced EOM-CCSD framework for calculations of excitation and ionization energies as well as state and transition properties (e.g., spectral intensities, natural transition, and Dyson orbitals) from both the ground and excited states. The errors in absolute excitation/ionization energies relative to the experimental reference data are on the order of 0.2–3.0 eV, depending on the K-edge considered and on the basis set used, and the shifts are systematic for each edge. Compared to a previously proposed CVS scheme where CVS was applied as a posteriori projection only during the solution of the EOM eigenvalue equations, the new scheme is computationally cheaper. It also achieves better cancellation of errors, yielding similar spectral profiles but with absolute core excitation and ionization energies that are systematically closer to the corresponding experimental data. Among the presented results are calculations of transient-state X-ray absorption spectra, relevant for interpretation of UV-pump/X-ray probe experiments.
151 citations
TL;DR: In this article, the rotational ground-state transition of the helium hydride ion HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC-7027 was detected.
Abstract: During the dawn of chemistry1,2, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With their higher ionization potentials, the helium ions He2+ and He+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe’s first molecular bond in the helium hydride ion HeH+ through radiative association with protons. As recombination progressed, the destruction of HeH+ created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH+ ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered3 as long ago as 1925, but only in the late 1970s was the possibility that HeH+ might exist in local astrophysical plasmas discussed4–7. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH+. Here we report observations, based on advances in terahertz spectroscopy8,9 and a high-altitude observatory10, of the rotational ground-state transition of HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC 7027. This confirmation of the existence of HeH+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination. Studies of the planetary nebula NGC 7027, using an upgraded spectrometer onboard a high-altitude observatory, have identified the rotational ground-state transition of the helium hydride ion—the first molecule to form after the Big Bang and an essential precursor to molecular hydrogen.
130 citations
TL;DR: In this article, the authors review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density.
Abstract: We review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density. We discuss the physics,...
123 citations
TL;DR: In this paper, the authors describe the behavior of hypersonic flows as energetic and result in regions of high temperature, causing internal energy excitation, chemical reactions, ionization, and gas surface interactions.
Abstract: Hypersonic flows are energetic and result in regions of high temperature, causing internal energy excitation, chemical reactions, ionization, and gas-surface interactions. At typical flight conditi...
119 citations
TL;DR: In this paper, a review of the use of emission lines for understanding galaxy evolution is presented, focusing on excitation source, metallicity, ionization parameter, ISM pressure and electron density.
Abstract: We review the use of emission-lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure and electron density. We show that the UV, optical and infrared contain complementary diagnostics that can probe the conditions within different nebular ionization zones. In anticipation of upcoming telescope facilities, we provide new self-consistent emission-line diagnostic calibrations for complete spectral coverage from the UV to the infrared. These diagnostics can be used in concert to understand how fundamental galaxy properties have changed across cosmic time. We describe new 2D and 3D emission-line diagnostics to separate the contributions from star formation, AGN and shocks using integral field spectroscopy. We discuss the physics, benefits, and caveats of emission-line diagnostics, including the effect of theoretical model uncertainties, diffuse ionized gas, and sample selection bias. Accounting for complex density gradients and temperature profiles is critical for reliably estimating the fundamental properties of H ii regions and galaxies. Diffuse ionized gas can raise metallicity estimates, flatten metallicity gradients, and introduce scatter in ionization parameter measurements. We summarize with a discussion of the challenges and major opportunities for emission-line diagnostics in the coming years.
TL;DR: This review attempts to present various developed techniques for the determination of the composition of noble metal NCs by ESI-MS and introduces advanced applications that use it to further understand the reaction mechanism, complexation behavior, and structure of nobleMetal NCs.
Abstract: Electrospray ionization mass spectrometry (ESI-MS) is an analytical technique that measures the mass of a sample through "soft" ionization. Recent years have witnessed a rapid growth of its application in noble-metal nanocluster (NC) analysis. ESI-MS is able to provide the mass of a noble-metal NC analyte for the analysis of their composition (n, m, q values in a general formula [Mn Lm ]q ), which is crucial in understanding their properties. This review attempts to present various developed techniques for the determination of the composition of noble metal NCs by ESI-MS. Additionally, advanced applications that use ESI-MS to further understand the reaction mechanism, complexation behavior, and structure of noble metal NCs are introduced. From the comprehensive applications of ESI-MS on noble-metal NCs, more possibilities in nanochemistry can be opened up by this powerful technique.
TL;DR: This study took the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest rovibronic quantum state at ultralow temperatures, thereby markedly reducing the number of exit channels accessible upon their mutual collision.
Abstract: Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. Here we take the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest ro-vibronic quantum state at ultralow temperatures, thereby drastically reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium molecules at a temperature of 500~nK, we directly observe reactants, intermediates, and products of the reaction $^{40}$K$^{87}$Rb + $^{40}$K$^{87}$Rb $\rightarrow$ K$_2$Rb$^*_2$ $\rightarrow$ K$_2$ + Rb$_2$. Beyond observation of a long-lived energy-rich intermediate complex, this technique opens the door to further studies of quantum-state resolved reaction dynamics in the ultracold regime.
TL;DR: In this article, the authors analyzed the C/O relationship for a combined sample of 40 galaxies with significant detections of the UV O+2/C+2 collisionally-excited lines and direct-method oxygen abundance measurements.
Abstract: Ultraviolet nebular emission lines are important for understanding the time evolution and nucleosynthetic origins of their associated elements, but the underlying trends of their relative abundances are unclear. We present UV spectroscopy of 20 nearby low-metallicity, high-ionization dwarf galaxies obtained using the Hubble Space Telescope. Building upon previous studies, we analyze the C/O relationship for a combined sample of 40 galaxies with significant detections of the UV O+2/C+2 collisionally-excited lines and direct-method oxygen abundance measurements. Using new analytic carbon ionization correction factor relationships, we confirm the flat trend in C/O versus O/H observed for local metal-poor galaxies. We find an average log(C/O) = -0.71 with an intrinsic dispersion of {\sigma} = 0.17 dex. The C/N ratio also appears to be constant at log(C/N) = 0.75, plus significant scatter ({\sigma} = 0.20 dex), with the result that carbon and nitrogen show similar evolutionary trends. This large and real scatter in C/O over a large range in O/H implies that measuring the UV C and O emission lines alone does not provide a reliable indicator of the O/H abundance. By modeling the chemical evolution of C, N, and O of individual targets, we find that the C/O ratio is very sensitive to both the detailed star formation history and to supernova feedback. Longer burst durations and lower star formation efficiencies correspond to low C/O ratios, while the escape of oxygen atoms in supernovae winds produces decreased effective oxygen yields and larger C/O ratios. Further, a declining C/O relationship is seen with increasing baryonic mass due to increasing effective oxygen yields.
TL;DR: In the early days of the universe, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH+, by radiative association with protons (He + H+ → HeH+ + hν) as discussed by the authors.
Abstract: During the dawn of chemistry1,2 when the temperature of the young Universe had fallen below ~4000 K, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With its higher ionization potentials, He++ (54.5 eV) and He+ (24.6 eV) combined first with free electrons to form the first neutral atom, prior to the recombination of hydrogen (13.6 eV). At that time, in this metal-free and low-density environment, neutral helium atoms formed the Universe’s first molecular bond in the helium hydride ion HeH+, by radiative association with protons (He + H+ → HeH+ + hν). As recombination progressed, the destruction of HeH+ (HeH+ + H → He + H2 +) created a first path to the formation of molecular hydrogen, marking the beginning of the Molecular Age.
TL;DR: In this article, the authors studied the global star-formation rate vs. stellar mass (SFR) vs. surface density (Sm) correlation in a sample of galaxies from the MaNGA MPL-5 survey and confirmed the existence of a Star-Forming Main Sequence (SFMS) for galaxies and spatially-resolved areas.
Abstract: We study the global star-formation rate (SFR) vs. stellar mass (M$_*$) correlation, and the spatially-resolved SFR surface density ($\Sigma_{SFR}$) vs. stellar mass surface density (\Sm) correlation, in a sample of $\sim2,000$ galaxies from the MaNGA MPL-5 survey. We classify galaxies and spatially-resolved areas into star-forming and retired according to their ionization processes. We confirm the existence of a Star-Forming Main Sequence (SFMS) for galaxies and spatially-resolved areas, and show that they have the same nature, with the global as a consequence of the local one. The latter presents a bend below a limit \Sm value, $\approx 3\times 10^7$ M$_\odot$kpc$^{-2}$, which is not physical. Using only star-forming areas (SFAs) above this limit, a slope and a scatter of $\approx1$ and $\approx0.27$ dex are determined. The retired galaxies/areas strongly segregate from their respective SFMS's, by $\sim -1.5$ dex on average. We explore how the global/local SFMS's depend on galaxy morphology, finding that for star-forming galaxies and SFAs, there is a trend to lower values of star-formation activity with earlier morphological types, which is more pronounced for the local SFMS. The morphology not only affects the global SFR due to the diminish of SFAs with earlier types, but also affects the local SF process. Our results suggest that the local SF at all radii is established by some universal mechanism partially modulated by morphology. Morphology seems to be connected to the slow aging and sharp decline of the SF process, and on its own it may depend on other properties as the environment.
TL;DR: The XENON1T detector as discussed by the authors is a dual-phase time projection chamber, which measures simultaneously the scintillation and ionization signals produced by interactions in target volume, to reconstruct energy and position, as well as the type of the interaction.
Abstract: The XENON1T experiment searches for dark matter particles through their scattering off xenon atoms in a 2 metric ton liquid xenon target. The detector is a dual-phase time projection chamber, which measures simultaneously the scintillation and ionization signals produced by interactions in target volume, to reconstruct energy and position, as well as the type of the interaction. The background rate in the central volume of XENON1T detector is the lowest achieved so far with a liquid xenon-based direct detection experiment. In this work we describe the response model of the detector, the background and signal models, and the statistical inference procedures used in the dark matter searches with a 1 metric ton×year exposure of XENON1T data, that leads to the best limit to date on WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6 GeV/c2.
TL;DR: In this paper, the HST COS spectra of 13 of the most highly ionized Green Pea (GP) galaxies were analyzed and correlations between Ly-alpha, galaxy properties, and low-ionization UV lines were investigated.
Abstract: As some of the only Lyman continuum (LyC) emitters at z~0, Green Pea (GP) galaxies are possible analogs of the sources that reionized the universe. We present HST COS spectra of 13 of the most highly ionized GPs, with [O III]/[O II]=6-35, and investigate correlations between Ly-alpha, galaxy properties, and low-ionization UV lines. Galaxies with high [O III]/[O II] have higher H-alpha equivalent widths (EWs), and high intrinsic Ly-alpha production may explain the prevalence of high Ly-alpha EWs among GPs. While Ly-alpha escape fraction is closely linked to low gas covering fractions, implying a clumpy gas geometry, narrow Ly-alpha velocity peak separation (delta_v,LyA) correlates with the ionization state, suggesting a density-bounded geometry. We therefore suggest that delta_v,LyA may trace the residual transparency of low-column-density pathways. Metallicity is associated with both [O III]/[O II] and delta_v,LyA. This trend may result from catastrophic cooling around low-metallicity star clusters, which generates a compact geometry of dense clouds within a low-density inter-clump medium. We find that the relative strength of low-ionization UV emission to absorption correlates with Ly-alpha emission strength and is related to Ly-alpha profile shape. However, as expected for optically thin objects, the GPs with the lowest delta_v,LyA show both weak low-ionization emission and weak absorption. The strengths of the low-ionization absorption and emission lines in a stacked spectrum do not correspond to any individual spectrum. Galaxies with high [O III]/[O II] contain a high fraction of LyC emitter candidates, but [O III]/[O II] alone is an insufficient diagnostic of LyC escape.
TL;DR: In this paper, the effects of the photon momentum in strong-field ionization were investigated using two counter-propagating laser pulses, and the high precision of the method and the intrinsically known zero momentum allowed them to unambiguously demonstrate the action of the light's magnetic field on the electron while it is under the tunnel barrier.
Abstract: When a strong laser pulse induces the ionization of an atom, momentum conservation dictates that the absorbed photons transfer their momentum to the electron and its parent ion. The sharing of the photon momentum between the two particles and its underlying mechanism in strong-field ionization, occurring when the bound electron tunnels through the barrier created by the superposition of the atomic potential and the electric laser field, are still debated in theory1–4 after 30 years of research. Corresponding experiments are very challenging due to the extremely small photon momentum and their precision has been too limited, so far, to ultimately resolve this debate5–8. By utilizing an experimental approach relying on two counter-propagating laser pulses, we present a detailed study of the effects of the photon momentum in strong-field ionization. The high precision of the method and the intrinsically known zero momentum allow us to unambiguously demonstrate the action of the light’s magnetic field on the electron while it is under the tunnel barrier, which has only been theoretically predicted so far1–3,9, thereby disproving opposing predictions5,10,11. Our results deepen the understanding of, for example, molecular imaging12,13 and time-resolved photoelectron holography14. Experiments with two counter-propagating laser beams report the observation that the photon momentum is shared between the electron and parent ion in strong-field ionization, which results from the photon’s magnetic field acting on the electron.
TL;DR: The state of the art regarding simulations of ionization equilibria of weak polyelectrolytes solutions and gels is recapitulates and gaps and open problems in the existing simulation literature are identified, and challenges for future development are proposed.
Abstract: This article recapitulates the state of the art regarding simulations of ionization equilibria of weak polyelectrolyte solutions and gels. We start out by reviewing the essential thermodynamics of ionization and show how the weak polyelectrolyte ionization differs from the ionization of simple weak acids and bases. Next, we describe simulation methods for ionization reactions, focusing on two methods: the constant-pH ensemble and the reaction ensemble. After discussing the advantages and limitations of both methods, we review the existing simulation literature. We discuss coarse-grained simulations of weak polyelectrolytes with respect to ionization equilibria, conformational properties, and the effects of salt, both in good and poor solvent conditions. This is followed by a discussion of branched star-like weak polyelectrolytes and weak polyelectrolyte gels. At the end we touch upon the interactions of weak polyelectrolytes with other polymers, surfaces, nanoparticles and proteins. Although proteins are an important class of weak polyelectrolytes, we explicitly exclude simulations of protein ionization equilibria, unless they involve protein-polyelectrolyte interactions. Finally, we try to identify gaps and open problems in the existing simulation literature, and propose challenges for future development.
TL;DR: In this article, the effects of the photon momentum in strong-field ionization were investigated using two counter-propagating laser pulses, and the high precision and self-referencing of the method allowed to unambiguously demonstrate the action of the light's magnetic field on the electron while it is under the tunnel barrier, confirming theoretical predictions, disproving others.
Abstract: When a strong laser pulse induces the ionization of an atom, momentum conservation dictates that the absorbed photons transfer their momentum $p_{\gamma}=E_{\gamma}/c$ to the electron and its parent ion. Even after 30 years of studying strong-field ionization, the sharing of the photon momentum between the two particles and its underlying mechanism are still under debate in theory. Corresponding experiments are very challenging due to the extremely small photon momentum ($~10^{-4}$ a.u.) and their precision has been too limited, so far, to ultimately resolve the debate. Here, by utilizing a novel experimental approach of two counter-propagating laser pulses, we present a detailed study on the effects of the photon momentum in strong-field ionization. The high precision and self-referencing of the method allows to unambiguously demonstrate the action of the light's magnetic field on the electron while it is under the tunnel barrier, confirming theoretical predictions, disproving others. Our results deepen the understanding of, for example, molecular imaging and time-resolved photoelectron holography.
TL;DR: It is found that all known X-ray spectroscopic observables can be fully and consistently described with continuous-distribution models of near-tetrahedral liquid water at ambient conditions with 1.74 ± 2.1% donated and accepted H-bonds per molecule, pointing to a continuous- distribution model.
Abstract: The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 ± 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray–matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open.
TL;DR: In this paper, the CO(2-1) and CO(3-2) molecular gas transitions and associated (sub)-mm continua of the nearby Seyfert 1.5 galaxy NGC3227 with angular resolutions 0.085-0.21" (7-15pc).
Abstract: We present ALMA observations of the CO(2-1) and CO(3-2) molecular gas transitions and associated (sub)-mm continua of the nearby Seyfert 1.5 galaxy NGC3227 with angular resolutions 0.085-0.21" (7-15pc). On large scales the cold molecular gas shows circular motions as well as streaming motions on scales of a few hundred parsecs associated with a large scale bar. We fitted the nuclear ALMA 1.3mm emission with an unresolved component and an extended component. The 850$\mu$m emission shows at least two extended components, one along the major axis of the nuclear disk and the other along the axis of the ionization cone. The molecular gas in the central region (1" ~73pc) shows several CO clumps with complex kinematics which appears to be dominated by non-circular motions. While we cannot demonstrate conclusively the presence of a warped nuclear disk, we also detected non-circular motions along the kinematic minor axis. They reach line-of-sight velocities of v-vsys =150-200km/s. Assuming that the radial motions are in the plane of the galaxy, then we interpret them as a nuclear molecular outflow due to molecular gas in the host galaxy being entrained by the AGN wind. We derive molecular outflow rates of $5\,M_\odot\,{\rm yr}^{-1}$ and $0.6\,M_\odot\,{\rm yr}^{-1}$ at projected distances of up to 30pc to the northeast and southwest of the AGN, respectively. At the AGN location we estimate a mass in molecular gas of $5\times 10^{5}\,M_\odot$ and an average column density $N({\rm H}_2) = 2-3\times 10^{23}\,{\rm cm}^{-2}$ in the inner 15pc. The nuclear molecular gas and sub-mm continuum emission of NGC3227 do not resemble the classical compact torus. Rather, these emissions extend for several tens of parsecs and appear connected with the circumnuclear ring in the host galaxy disk, as found in other local AGN. (Abridged)
Spanish National Research Council1, University of Oxford2, Max Planck Society3, PSL Research University4, University of Copenhagen5, University of Arizona6, Diego Portales University7, University of Southampton8, University of Alaska Anchorage9, INAF10, Graduate University for Advanced Studies11, National Institutes of Natural Sciences, Japan12, Space Telescope Science Institute13, Liverpool John Moores University14, University of Texas at San Antonio15, University of La Laguna16, Peking University17, Durham University18, Ludwig Maximilian University of Munich19
TL;DR: In this paper, the CO(2−1) and CO(3−2) molecular gas transitions and associated (sub-) millimeter continua of the nearby Seyfert 1.5 galaxy NGC 3227 with angular resolutions 0.085−0.21″ (7−15 pc).
Abstract: ALMA observations have revealed nuclear dusty molecular disks or tori with characteristic sizes 15−40 pc in the few Seyferts and low -luminosity AGN that have been studied so far. These structures are generally decoupled both morphologically and kinematically from the host galaxy disk. We present ALMA observations of the CO(2–1) and CO(3–2) molecular gas transitions and associated (sub-) millimeter continua of the nearby Seyfert 1.5 galaxy NGC 3227 with angular resolutions 0.085 − 0.21″ (7–15 pc). On large scales, the cold molecular gas shows circular motions as well as streaming motions on scales of a few hundred parsecs that are associated with a large-scale bar. We fit the nuclear ALMA 1.3 mm emission with an unresolved component and an extended component. The 850 μm emission shows at least two extended components, one along the major axis of the nuclear disk, and the other along the axis of the ionization cone. The molecular gas in the central region (1″ ∼ 73 pc) shows several CO clumps with complex kinematics that appears to be dominated by noncircular motions. While we cannot conclusively demonstrate the presence of a warped nuclear disk, we also detected noncircular motions along the kinematic minor axis. They reach line-of-sight velocities of v − vsys = 150 − 200 km s−1. Assuming that the radial motions are in the plane of the galaxy, we interpret them as a nuclear molecular outflow due to molecular gas in the host galaxy that is entrained by the AGN wind. We derive molecular outflow rates of 5 M⊙ yr−1 and 0.6 M⊙ yr−1 at projected distances of up to 30 pc to the northeast and southwest of the AGN, respectively. At the AGN location we estimate a mass in molecular gas of 5 × 105 M⊙ and an equivalent average column density N(H2) = 2 − 3 × 1023 cm−2 in the inner 15 pc. The nuclear CO(2–1) and CO(3–2) molecular gas and submillimeter continuum emission of NGC 3227 do not resemble the classical compact torus. Rather, these emissions extend for several tens of parsecs and appear connected with the circumnuclear ring in the host galaxy disk, as found in other local AGN.
TL;DR: In this paper, the authors derived new self-consistent theoretical diagnostics for the ISM pressure and electron density in the ionized nebulae of star-forming galaxies.
Abstract: We derive new self-consistent theoretical UV, optical, and IR diagnostics for the ISM pressure and electron density in the ionized nebulae of star-forming galaxies Our UV diagnostics utilize the inter-combination, forbidden and resonance lines of silicon, carbon, aluminum, neon, and nitrogen We also calibrate the optical and IR forbidden lines of oxygen, argon, nitrogen and sulfur We show that line ratios used as ISM pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas In addition, the traditional electron density diagnostic [S II] {\lambda}6731/[S II] {\lambda}6717 is strongly dependent on the gas-phase metallicity We show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae The [S II] and [O II] ratios are produced in different zones, and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant We review the temperature and density distributions observed within H II regions and discuss the implications of these distributions on measuring the electron density of the gas Many H II regions contain radial variations in density We suggest that the ISM pressure is a more meaningful quantity to measure in H II regions or galaxies Specific combinations of line ratios can cover the full range of ISM pressures (4 < log(P/k) < 9) As H II regions become resolved at increasingly high redshift through the next generation telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day
TL;DR: Spin selectivity in photo-emission from ferromagnetic substrates functionalized with chiral organic films was analyzed by ultraviolet photoelectron spectroscopy at room temperature and spectral widths were found to depend on substrate magnetization orientation and polarization, which are attributed to helicity-dependent molecular ionization cross sections arising from photoelectrons impact.
Abstract: Spin selectivity in photo-emission from ferromagnetic substrates functionalized with chiral organic films was analyzed by ultraviolet photoelectron spectroscopy at room temperature. Using radiation with photon energy greater than the ionization potential of the adsorbed molecules, photoelectrons were collected that originated from both underlying ferromagnetic substrates and the organic films, with kinetic energies in the range of ca. 0-18 eV. We investigated chiral organic films composed of self-assembled monolayers of α-helical peptides and electrostatically adsorbed films of the protein, bovine serum albumin, with different α-helix and β-sheet contents. Ultraviolet photoelectron spectral widths were found to depend on substrate magnetization orientation and polarization, which we attribute to helicity-dependent molecular ionization cross sections arising from photoelectron impact, possibly resulting in spin-polarized holes. These interactions between spin-polarized photoelectrons and chiral molecules are physically manifested as differences in the measured photoionization energies of the chiral molecular films. Substrate magnetization-dependent ionization energies and work function values were deconvoluted using surface charge neutralization techniques, permitting the measurement of relative spin-dependent energy barriers to transmission through chiral organic films.
TL;DR: This review summarizes the most important features of tandem mass spectra generated by collision-induced dissociation fragmentation and presents didactic examples for the unexperienced users.
Abstract: Tandem mass spectrometry is an important tool for structure elucidation of natural and synthetic organic products. Fragmentation of odd electron ions (OE⁺) generated by electron ionization (EI) was extensively studied in the last few decades, however there are only a few systematic reviews available concerning the fragmentation of even-electron ions (EE⁺/EE-) produced by the currently most common ionization techniques, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). This review summarizes the most important features of tandem mass spectra generated by collision-induced dissociation fragmentation and presents didactic examples for the unexperienced users.
TL;DR: In this paper, orientation-dependent stereo Wigner time delays of CO molecules are used to reveal the electron localization at the ionization moment, which constitutes a spatially and temporally-resolved reconstruction of the molecular photoelectric effect.
Abstract: We present orientation-dependent stereo Wigner time delays of CO molecules, which reveal the electron localization at the ionization moment. Together with theoretical calculations this constitutes a spatially-and temporally-resolved reconstruction of the molecular photoelectric effect.
TL;DR: In this article, the electric field in a fast ionization wave discharge in a diffuse nanosecond pulse discharge plasma in atmospheric pressure air is measured using the Electric Field Induced Second Harmonic (E-FISH) diagnostic.
Abstract: The time-resolved electric field in a fast ionization wave discharge in a diffuse nanosecond pulse discharge plasma in atmospheric pressure air is measured using the Electric Field Induced Second Harmonic (E-FISH) diagnostic. The electric field is placed on an absolute scale by calibration against a Laplacian field. At relatively low peak voltages, when the plasma is generated only near the pin high-voltage electrode, the electric field is measured ahead of the ionization wave during the entire voltage pulse, exhibiting a strong field enhancement compared to the Laplacian field, by about an order of magnitude. As the peak voltage is increased and the ionization wave traverses the laser beam, the electric field is measured both ahead of the wave and behind the ionization front, where the field drops rapidly due to the charge separation and plasma selfshielding. When the wave reaches the grounded electrode, the discharge transitions into a conduction phase in which the potential is redistributed within the gap. The electric field in the vicinity of the pin then increases again, following the applied voltage waveform for the rest of the pulse. The effective time resolution of the present measurements is 150 ps. Based on the single shot data, we find that the peak electric field in the wave front is moderately influenced by the applied voltage and varies between 160 to 210 kV/cm. This study demonstrates the viability of the E-FISH diagnostic for this class of atmospheric pressure discharges and paves the way for future in-depth studies of this particular problem.
TL;DR: In this article, the spectra become nebular within 2-4 $e$-folding times after light curve peak, with the rate of spectroscopic evolution correlated to the light curve timescale.
Abstract: We study the spectroscopic evolution of superluminous supernovae (SLSNe) later than 100 days after maximum light. We present new data for Gaia16apd and SN2017egm, and analyse these with a larger sample comprising 41 spectra of 12 events. The spectra become nebular within 2-4 $e$-folding times after light curve peak, with the rate of spectroscopic evolution correlated to the light curve timescale. Emission lines are identified with well-known transitions of oxygen, calcium, magnesium, sodium and iron. SLSNe are differentiated from other Type Ic SNe by a prominent O I $\lambda$7774 line and higher-ionisation states of oxygen. The iron-dominated region around 5000 A is more similar to broad-lined SNe Ic than to normal SNe Ic. Principal Component Analysis shows that 5 `eigenspectra' capture 75% of the variance, while a clustering analysis shows no clear evidence for multiple SLSN sub-classes. Line velocities are 5000--8000 km/s, and show stratification of the ejecta. O I $\lambda$7774 likely arises in a dense inner region that also produces calcium emission, while [O I] $\lambda$6300 comes from further out until 300--400 days. The luminosities of O I $\lambda$7774 and Ca II suggest significant clumping, in agreement with previous studies. Ratios of [Ca II]$\lambda$7300/[O I]$\lambda$6300 favour progenitors with relatively massive helium cores, likely $\gtrsim 6$ M$_\odot$, though more modelling is required here. SLSNe with broad light curves show the strongest [O I] $\lambda$6300, suggesting larger ejecta masses. We show how the inferred velocity, density and ionisation structure point to a central power source.