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•This work deals with a long standing issue in ion-surface interaction, namely the dominant excitation of the triplet state Ne**2p4(3P)3s2 in neon colliding with slightly heavier ...targets Mg, Al and Si.•We perform angle resolved measurements of electron spectra from autoionization of the triplet Ne**2p4(3P)3s2 and the singlet Ne**2p4(1D)3s2 excited states of Neon projectiles scattered from Al and Mg surfaces.•The measurements support the physical picture of an Auger rearrangement that occurs while the colliding atoms are still coupled in the quasi-molecular system.•Our study show the importance of electron correlation effects in determining the charge and excitation state of scattered projectiles.
We address the long standing issue of the dominant excitation of the triplet 2p4(3P)3s2 state in the scattering of Neon projectiles from Magnesium, Aluminum and Silicon surfaces, which is not predicted by the Fano-Lichten Molecular orbital promotion model. We measured autoionization spectra from the triplet and the singlet states of Neon excited at Al and Mg surfaces. The measurements show that the triplet excited state is produced locally at the collision site, supporting the physical picture of an Auger rearrangement converting the singlet state into the triplet while the colliding atoms are still coupled in the quasi-molecular system.
We report energy distributions of electrons emitted by Aluminum and Magnesium surfaces under the impact of singly charged neon ions with energies in the range 100–5000 eV, focusing on the Auger decay ...of electronic excitations produced during binary atomic collisions. The autoionization spectra of the projectiles show several peaks that are identified and assigned to specific collisional excitation processes. The data provide evidence for electron correlation effect that occur while the colliding atoms are still coupled in the quasi-molecular system and results in two-electron transitions.
CHIANTI contains a large quantity of atomic data for the analysis of astrophysical spectra. Programs are available in IDL and Python to perform calculation of the expected emergent spectrum from ...these sources. The database includes atomic energy levels, wavelengths, radiative transition probabilities, rate coefficients for collisional excitation, ionization, and recombination, as well as data to calculate free-free, free-bound, and two-photon continuum emission. In Version 9, we improve the modeling of the satellite lines at X-ray wavelengths by explicitly including autoionization and dielectronic recombination processes in the calculation of level populations for select members of the lithium isoelectronic sequence and Fe xviii-xxiii. In addition, existing data sets are updated, new ions are added, and new total recombination rates for several Fe ions are included. All data and IDL programs are freely available at http://www.chiantidatabase.org or through SolarSoft, and the Python code ChiantiPy is also freely available at https://github.com/chianti-atomic/ChiantiPy.
The ionization dynamics of helium droplets irradiated by intense, femtosecond extreme ultraviolet (XUV) pulses is investigated in detail by photoelectron spectroscopy. Helium droplets are resonantly ...excited to atomic-like 2p states with a photon energy of 21.5 eV and autoionize by interatomic Coulombic decay (ICD). A complex evolution of the electron spectra as a function of droplet size (250 to 106 He atoms per droplet) and XUV intensity (109-1012 W cm−2) is observed, ranging from narrow atomic-like peaks that are due to binary autoionization, to an unstructured feature characteristic of electron emission from a nanoplasma. The experimental results are analyzed and interpreted with the help of a numerical simulation based on rate equations taking into account all relevant processes-multi-step ionization, electronic relaxation, ICD, secondary inelastic collisions, desorption of electronically excited atoms, and collective autoionization (CAI).
Water surface is acidic Buch, Victoria; Milet, Anne; Vácha, Robert ...
Proceedings of the National Academy of Sciences - PNAS,
05/2007, Volume:
104, Issue:
18
Journal Article
Peer reviewed
Open access
Water autoionization reaction 2H₂O rightward arrow H₃O⁻ + OH⁻ is a textbook process of basic importance, resulting in pH = 7 for pure water. However, pH of pure water surface is shown to be ...significantly lower, the reduction being caused by proton stabilization at the surface. The evidence presented here includes ab initio and classical molecular dynamics simulations of water slabs with solvated H₃O⁺ and OH⁻ ions, density functional studies of (H₂O)₄₈H⁺ clusters, and spectroscopic isotopic-exchange data for D₂O substitutional impurities at the surface and in the interior of ice nanocrystals. Because H₃O⁺ does, but OH⁻ does not, display preference for surface sites, the H₂O surface is predicted to be acidic with pH < 4.8. For similar reasons, the strength of some weak acids, such as carbonic acid, is expected to increase at the surface. Enhanced surface acidity can have a significant impact on aqueous surface chemistry, e.g., in the atmosphere.
Alkaline earth Rydberg atoms are very promising tools for quantum technologies. Their highly excited outer electron provides them with the remarkable properties of Rydberg atoms and, notably, with a ...huge coupling to external fields or to other Rydberg atoms while the ionic core retains an optically active electron. However, low angular-momentum Rydberg states suffer almost immediate autoionization when the core is excited. Here, we demonstrate that strontium circular Rydberg atoms with a core excited in a 4D metastable level are impervious to autoionization over more than a few millisecond time scale. This makes it possible to trap and laser-cool Rydberg atoms. Moreover, we observe singlet to triplet transitions due to the core optical manipulations, opening the way to a microwave to optical quantum interface.
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•The doubly excited 1Po resonance states in H−and Ps− are studied.•Variational methods and correlated exponential wavefunctions are used.•Resonance positions, widths, autoionization ...decay rates are calculated.•Oscillator strengths (OS) and radiative decay rates are reported.•The ratios of OS between the Feshbach and shape resonances are presented.
The autoionization decay (AD) and radiative decay (RD) for doubly excited 1Po resonance states in H− and Ps− are studied using correlated exponential wavefunctions based on the variational methods. To trace the resonance poles from Ps− to H−, the nuclear mass is varied from one unit to infinitely heavy. Resonance positions, widths related to AD rates, oscillator strengths, the ratios of oscillator strengths between the Feshbach and shape resonances (FSR), RD rates for the lowest two FSR in the 1Po spectrum, are reported. Few results are new, and others are comparable with the available theoretical and experimental data.
The Dakin and Baeyer-Villiger (BV) oxidation reactions require addition of peroxides as oxidants and an acid or a base as a catalyst. Reaction times range from hours to days to obtain target ...products. Previously, we reported that hydrogen peroxide (H
2
O
2
) is spontaneously generated in water microdroplets without any added chemicals or applied electrical potential. Here, we report that the Dakin and BV reactions occur in modest yields within milliseconds in aqueous microdroplets at room-temperature without the addition of external peroxides and catalysts. H
2
O
2
generation is the result of the special environment of the microdroplet surface, which promotes water autoionization. We find that increasing the content of water and decreasing the droplet size improve the product yield of the Dakin and BV reactions, supporting the contention that the amount of H
2
O
2
generated in aqueous microdroplets could induce the two reactions and the reactions occur at or near the air-water interface of the microdroplet surface.
The Dakin and Baeyer-Villiger (BV) oxidation reactions require addition of peroxides as oxidants and an acid or a base as a catalyst.
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of ...autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20-40 eV spectral range, in the vicinity of the 3s
np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
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