Theory Of Ionization Research Articles

Electrochemical conversion of solid Nb2O5 to Nb in sodium chloride melt as proof of oxygen ionisation mechanism of electrodeoxidation

The direct electrochemical reduction of a solid metal oxide (MOx) to metal (M) in calcium chloride melt (FFC Cambridge process) has been proposed to take place via. oxygen ionisation mechanism, MOx + 2xe− → M + xO2−. However, generation of calcium metal and reduction of the oxide with it too becomes possible under the applied potential condition (3.1 V) of an FFC cell. The unique chemistry of calcium chloride melt, upon cathodic polarisation, makes it difficult to distinguish between the reduction by electrons and calcium metal. Hence in order to confirm the oxygen ionisation theory of electro-deoxidation, electrochemical deoxidation experiments were carried out with sintered Nb2O5 pellet electrodes in molten sodium chloride at 1173 K. The pellets were found reduced to Nb metal. Sodiothermic reduction of Nb2O5 is thermodynamically not feasible (Nb2O5 + 10Na → 5Na2O + 2Nb, ΔG°1173K = 102.1 kJ) and hence the observed reduction of the oxide is attributed to electrons. This study, for the first time, gives reliable experimental evidence to the oxygen ionisation mechanism of electro-reduction of solid oxides in the FFC process. The experimental results also prove that the electro-reduction of oxides can occur in melts, which otherwise were considered unsuitable from thermodynamic considerations.

Integral-equation approach to the weak-field asymptotic theory of tunneling ionization

An integral equation approach to the weak-field asymptotic theory (WFAT) of tunneling ionization is developed. An integral representation for the exact partial amplitudes of ionization into parabolic channels is derived. The WFAT expansion for the ionization rate follows immediately from this relation. Integral representations for the coefficients in the expansion are obtained. The integrals accumulate where the ionizing orbital has large amplitude and are not sensitive to its behavior in the asymptotic region. Hence, these formulas enable one to reliably calculate the WFAT coefficients even if the orbital is represented by an expansion in Gaussian basis, as is usually the case in standard software packages for electronic structure calculations. This development is expected to greatly simplify the implementation of the WFAT for polyatomic molecules, and thus facilitate its growing applications in strong-field physics.

Физическая химия и физика металлургических систем

Yttrium belongs to the same group as lanthanum, and its chemical properties are close to those of the latter. Therefore, yttrium is referred to as a rare earth metal. When added to a heavily deoxidized metal, yttrium refines a primary cast grain, reduces the area of treeing, purifies grain boundaries of non-ferrous inter-metallic compounds, reduces the size of non-metallic inclusions, and enhances heat resistance and high temperature strength of special steels. Optimal yttrium additive in the metal does not exceed 0.3 to 0.5 wt. %. Complex interaction of yttrium with oxygen in the presence of residual concentrations of aluminum, calcium and magnesium in the metal was not studied at all. Thermodynamic modelling of steel deoxidation using yttrium in the presence of low concentrations of aluminum, calcium or magnesium is developed. The surfaces of component solubility in liquid steel are created for Fe–Y–Al–O–C, Fe–Y–Ca–O–C, and Fe–Y–Mg–O–C systems. To make calculations related to oxide systems, all possible phase equilibria are established, coordination of equilibrium constants dependency on temperature is carried out, and energy parameters of the subregular ionic solution theory are specified. The surfaces of component solubility show that deoxidation by yttrium is a complex process due to the presence of calcium and aluminum in steel. Deoxidation products will contain complex phase compositions of oxides based on CaO, Al 2 O 3 , and Y 2 O 3 . In case of steel deoxidation by yttrium and magnesium, the process is performed alternately. Either yttrium or magnesium acts as a deoxidizer.

Relation between Electrical Conductivity and Viscosity of CaO–SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub>–MgO System

Alternating current impedance method has been used to measure the electrical conductivity of CaO–SiO2–Al2O3–MgO system and viscosity of this system has been measured by high temperature rheometer at the same time. It is found that measured data of electrical conductivity and viscosity showed a relatively high accuracy. A relation between the two parameters has been estimated using a formula which showed a relatively lower deviation compared to the precious work. Ionization theory of molten slag has been used to explicate the electrical conductivity and viscosity of molten slag.

A note on the falsification of the ionic theory of hair cell transduction

A note on the falsification of the ionic theory of hair cell transduction

Charge-state dependence of inner-shell processes in collisions between highly charged Xe ions and solids at intermediate energies

The x-ray emission during the penetration of 2--6 MeV ${\mathrm{Xe}}^{q+}$ ($q=20,22,26,30$) ions into thick solid targets of iron and nickel has been measured. An obvious charge-state and incident-energy dependence of the target-to-projectile vacancy-production cross-section ratios was found for the iron target but not for the nickel target. The results are supported by the vacancy-sharing model and direct ionization theory and imply the great importance of level matching for the inner-shell process. The charge equilibration time of ${\mathrm{Xe}}^{30+}$ in solid iron was derived to be around 9 fs from the measured x-ray yields.

Modification of the quantum mechanical flux formula for electron-hydrogen ionization through Bohm's velocity field

For the single differential cross section (SDCS) for hydrogen ionization by electron impact ($e$-H problem), we propose a correction to the flux formula given by R. Peterkop [Theory of Ionization of Atoms by Electron Impact (Colorado Associated University Press, Boulder, 1977)]. The modification is based on an alternative way of defining the kinetic energy fraction, using Bohm's definition of velocities instead of the usual asymptotic kinematical, or geometrical, approximation. It turns out that the solution-dependent, modified energy fraction is equally related to the components of the probability flux. Compared to what is usually observed, the correction yields a finite and well-behaved SDCS value in the asymmetrical situation where one of the continuum electrons carries all the energy while the other has zero energy. We also discuss, within the $S$-wave model of the $e\ensuremath{-}\mathrm{H}$ ionization process, the continuity of the SDCS derivative at the equal energy sharing point, a property not so clearly observed in published benchmark results obtained with integral and $S$-matrix formulas with unequal final states.

Analysis on laser-induced transient damage behavior in multilayer coating

Based on the ionization theory and the Drude model of free electron gas, transient damage principle of the anti-reflection coating under ultrashort pulses are analyzed. Specifically, the damage of an anti-reflection coating designed by ZnS/SiO2 materials is calculated. The results show that during the irradiation process the parameters, such as the refractive index, the electric field and the free electron density, should impact on each other. The coupling relationship between these parameters causes the change in the refractive index, which further leads to the decrease of transmittance of anti-reflection coating from 0.96 to 0.01. In addition, the coupling relationship causes the repartition of free electron density constantly, which eventually leads to the external damage of anti-reflection coating.

Interfering one-photon and two-photon ionization by femtosecond VUV pulses in the region of an intermediate resonance

The electron angular distribution after atomic photoionization by the fundamental frequency and its second harmonic is analyzed for a case when the frequency of the fundamental scans the region of an intermediate atomic state. The angular distribution and its left-right asymmetry, due to the two-pathway interference between nonresonant one-photon and resonant two-photon ionization, sharply change as a function of the photon energy. The phenomenon is exemplified by both solving the time-dependent Schr\odinger equation on a numerical space-time grid and by applying perturbation theory for ionization of the hydrogen atom in the region of the $1s\text{\ensuremath{-}}2p$ transition for femtosecond pulses as well as an infinitely long exposure to the radiation. Parametrizations for the asymmetry and the anisotropy coefficients, obtained within perturbation theory, reveal general characteristics of observable quantities as functions of the parameters of the radiation beam.

Weak-field asymptotic theory of tunneling ionization including the first-order correction terms: Application to molecules

The weak-field asymptotic theory (WFAT) of tunneling ionization including the first-order correction terms is validated for molecules by comparison with accurate calculations of molecular Siegert states in a static electric field. Both fundamental observables related to tunneling ionization, namely, the ionization rate and transverse momentum distribution of the ionized electrons, are considered. This complements our previous study of atoms [V. H. Trinh et al., Phys. Rev. A 87, 043426 (2013)]. Similarly to the atomic case, the first-order terms essentially improve the agreement between the WFAT and accurate results in a wide interval of fields up to the onset of over-the-barrier ionization. This establishes the WFAT including the first-order correction terms as an appealing alternative to accurate calculations in the tunneling regime. In addition to demonstrating the quantitative performance of the WFAT, the theory is shown to be helpful for understanding the field and orientation dependencies of the observables. In particular, we show that the first-order terms account for a deviation of the shape of the orientation dependence of the ionization rate of a molecule from that of the ionizing orbital as the field grows, which has important implications for strong-field molecular imaging techniques. This prediction of the WFAT is confirmed by comparison with time-dependent calculations.

On the Theory of Hydrogen Atom Ionization by Ultra‐Short Electromagnetic Pulses

AbstractAn investigation of the probability of hydrogen atom ionization by ultra‐short electromagnetic pulses is carried out in the frame of perturbation theory We consider the case when the electric field strength amplitude E0 in a pulse by two orders lower than characteristic atomic field strength Ea (Ea ≅ 5.1 · 109 V/cm). A detailed investigation of the dependence of the probabilities on the pulse duration was performed for Gaussian pulse shapes. In the case where the carrier frequency of the Gaussian pulse is larger than the atomic ionization potential, the probability goes to the standard limit of perturbation per unit time. At the same pulse durations, the probabilities for carrier frequencies less than the ionization potential go to zero. The frequency dependence of the ionization probability becomes equal to the standard threshold dependence with increasing pulse duration time. A comparison between the ionization effects caused by wavelet pulses without carrier frequency and Gaussian pulses with carrier frequency shows that the same ionization probability values are achieved when the pulse carrier frequency is detuned by about 20% from the ionization threshold. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Green-function approach to the theory of tunneling ionization

We solve the problem of tunneling ionization of a multielectron atom in a static electric field by using the Green's function for the Stark-Coulomb problem. This allows us to incorporate the outgoing-wave boundary conditions at infinity. The interaction of the active electron with the atomic residue is described either by a model potential or by the $l$-dependent pseudopotential which prevents virtual transitions to orbitals occupied by inner electrons. The method works well in the broad range of electric fields including the region above the classical ionization threshold (the barrier-suppression region). Calculations of ionization of Ar demonstrate a noticeable difference between the model potential approach and the pseudopotential approach, but both sets of results agree with experimental data.

Charge transport-accumulation in multilayer structures with Si3N4 and thick(5.5 nm) SiO2

Double-injection, transport, and accumulation of charge in metal-thick oxide-nitride-silicon and silicon-tunnel oxide-nitride-thick oxide-silicon structures have been theoretically studied. Calculation results were compared to experimental results. The charge transport in Si3N4 is quantitatively described assuming the multiphonon ionization theory of neutral traps with a capture cross-section less than 10−14 cm2. With traps amphoterism taken into account, the calculation predicts the existence of a layer with their excessive concentration near the SiO2/Si3N4 interface. The model satisfactorily describes the write/erase characteristics in silicon-oxide-nitride-oxide-silicon-structures from Bu and White (Solid-State Electron. 45, 113 (2001)).

Weak-field asymptotic theory of tunneling ionization: benchmark analytical results for two-electron atoms

The recently developed many-electron weak-field asymptotic theory of tunneling ionization of atoms and molecules in an external static electric field (Tolstikhin et al 2014, Phys. Rev. A 89, 013421) is extended to the first-order terms in the asymptotic expansion in field. To highlight the results, here we present a simple analytical formula giving the rate of tunneling ionization of two-electron atoms H− and He. Comparison with fully-correlated ab initio calculations available for these systems shows that the first-order theory works quantitatively in a wide range of fields up to the onset of over-the-barrier ionization and hence is expected to find numerous applications in strong-field physics.

Quantum-orbit theory of low-energy above-threshold ionization on and off axis

Intense-laser-induced above-threshold ionization of a bound electron into continuum states with low energy is investigated in the context of the strong-field approximation that allows for one act of rescattering of the revisiting electron. The quantum orbits for forward and backward scattering are evaluated and generalized to arbitrary scattering angles. The velocity map of the liberated electron exhibits the well-known low-energy structure as well as other features off the polarization axis.

Electron Impact Ionization of Metastable 3S-State Hydrogen Atoms by Electrons in Coplanar Geometry

In this work we have calculated first born triple differential cross sections (TDCS) for ionization of metastable 3S- state hydrogen atoms by electrons. In this study the final state wave function is described by a multiple scattering theory for ionization of hydrogen atoms by electrons. Results show qualitative agreement with other existing theoretical results for ionization of hydrogen atoms from metastable 2S-state and 2P-state. There are no other available results for ionization of hydrogen atoms from metastable 3S-state. The present result offers an extensive scope for experimental verifications in such ionization process.

Современное развитие теории нелинейной ионизации атомов и ионов

Современное развитие теории нелинейной ионизации атомов и ионов, Карнаков Б.М., Мур В.Д., Попруженко С.В., Попов В.С.

Современное развитие теории нелинейной ионизации атомов и ионов

Современное развитие теории нелинейной ионизации атомов и ионов, Карнаков Б.М., Мур В.Д., Попруженко С.В., Попов В.С.

Современное развитие теории нелинейной ионизации атомов и ионов

Современное развитие теории нелинейной ионизации атомов и ионов

Low-frequency approximation for above-threshold ionization by a laser pulse: Low-energy forward rescattering

In the context of the development of new sources of strong laser pulses in the mid-infrared region new nonperturbative methods for analysis of strong-laser-field induced or assisted atomic and molecular processes are welcome. We formulate such a theory of above-threshold ionization by a strong low-frequency laser pulse. We call this theory the low-frequency approximation (LFA). A detailed derivation of the LFA, both for short and long laser pulses, is given. As an example the LFA is applied to the analysis of recently discovered low-energy structures in the above-threshold ionization spectra of atoms ionized by long-wavelength laser pulses. It was found that these low-energy structures are caused by the forward soft recollision of the ionized electrons with the parent ion which is enhanced by the Coulomb effect.