Ionization Of Neon Research Articles

Evidence of strong projectile–target-core interaction in single ionization of neon by electron impact

The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile--target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

Nonsequential Two-Photon Double Ionization of Atoms: Identifying the Mechanism

We develop an approximate model for the process of direct (nonsequential) two-photon double ionization of atoms. Employing the model, we calculate (generalized) total cross sections as well as energy-resolved differential cross sections of helium for photon energies ranging from 39 to 54 eV. A comparison with results of ab initio calculations reveals that the agreement is at a quantitative level. We thus demonstrate that this complex ionization process can be described by the simple model, providing insight into the underlying physical mechanism. Finally, we use the model to calculate generalized cross sections for the two-photon double ionization of neon in the nonsequential regime.

Absolute triple-differential cross sections for intermediate energy electron impact ionization of neon and argon

Absolute triple-differential cross sections for intermediate energy electron impact ionization of neon and argon are reported. The data highlight ongoing challenges for theory in the description of this ionization problem and the immense value of absolute measurements over relative data in guiding the ongoing development of theory.

Electron parameters in Xe-Ne mixtures

The effect made by xenon concentration and by reduced electric field on the parameters of electrons in Xe-Ne mixtures is numerically studied. It is demonstrated that the increase in xenon concentration in mixture leads to a decrease in the average electron energy, to an increase in the frequency of collisions of electrons with gas atoms, and to variation of the transport coefficients of electrons. The increase in xenon concentration in mixture above ≈10% leads to an abrupt slowing down of the rates of excitation of xenon atoms. The efficiency of ionization increases with the xenon concentration increasing to ≈7%. The fraction of electron energy spent for excitation of xenon decreases with increasing electric field, and more energy is put into the ionization of xenon and into excitation and ionization of neon. The results of calculation of parameters of electrons make it possible to limit the search for xenon concentrations in Xe-Ne mixture, which are optimal for vacuum ultraviolet radiation, to the range of 1–10%.

Single ionization of Ne, Ar and Kr by proton impact: Single differential distributions in energy and angle

In this work we present a theoretical study of singly differential cross sections in energy and angle for the single ionization of neon, argon and krypton by proton impact. Theoretical results obtained by means of the Continuum Distorted Wave-Eikonal initial state (CDW-EIS) model are compared to those provided by the First Born Approximation (FBA) and the classical trajectory Monte Carlo (CTMC) method as well as to experimental data from several laboratories. We note in particular for argon, that the CDW-EIS model does not reproduce the experimental data as accurately as expected, while the CTMC instead is in very good agreement.

Photoelectron angular correlation pattern in sequential two-photon double ionization of neon

We apply an angular momentum coupling formalism to describe the angular correlation pattern in sequential two-photon double ionization of neon. Comparison with previous work (Fritzsche et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 165601) reveals some important differences which are discussed in terms of various ionization mechanisms and their theoretical implementations in two alternative approaches.

Near-threshold electron impact doubly differential cross sections for the ionization of neon and xenon

Normalized doubly differential cross sections (DDCSs) for the electron impact single ionization of Ne and Xe are presented. The Ne measurements are taken at incident energies of 23.5 eV, 25 eV, 30 eV and 40 eV while the Xe measurements are taken at 14 eV, 15 eV and 20 eV. Scattering angles in the experiment range from 15° to 120°. The measurements use a moveable target method for an accurate determination of the experimental background. Normalization of the differential data is initially made to available experimental cross sections for excitation of the ground np6 to the np5 (n + 1)s excited states of the noble gas and then, if necessary after integration, to available experimental total ionization cross sections. We show that our single differential cross sections, derived from integrating the DDCSs, show a convex profile (frown) for Ne whereas they are concave (smile) for Xe similar to what is observed for He and we suggest a tentative mechanism for this effect.

Fully differential cross-section measurements for electron-impact ionization of neon and xenon

We present a combined experimental and theoretical investigation of the fully differential cross section for electron-impact ionization of neon and xenon. The experiments were performed under coplanar asymmetric kinematics, at intermediate incident electron energies, and for a range of scattered electron detection angles. The experimental results are compared with three calculations: a convergent close-coupling calculation, a distorted-wave Born approximation (DWBA) calculation with inclusion of the Gamow factor, and a hybrid $\mathrm{DWBA}+R$-matrix calculation. The comparison between the experimental and theoretical results highlights the importance of the description of postcollision interaction, and the results exhibit interesting orbital-dependent differences.

Screening effects and total cross sections of single, double and triple ionization of neon by fast electrons

The Bethe–Born theory is applied to estimate the effective charges experienced by the ejected electrons at single, double and triple ionization of neon by fast electrons. The expansion coefficients appearing in the asymptotic expressions for total cross sections σn+ ∼ [an+ln(Ei/In+) + bn+]/Ei are determined by fitting to these expressions the experimental data for single and multiple ionization of neon. Coefficients an+ and bn+ are seen to decrease exponentially with increasing number of ejected electrons. Empirical formulae are found to describe this behaviour. Analytical expressions for coefficients an+ are derived within the Bethe–Born approximation for single, double and triple ionization of neon. The effective charges are determined by assuming that the derived analytical expressions for an+ can be reduced to the empirical formula. It is shown that, in order to obtain the reasonable values for the effective charges, coefficient bn+ should be taken into consideration. It is also revealed that the inclusion of interaction between the ejected electrons in the final state in calculation improves the results.

Pump-probe studies of autoionizing states of noble gases combining laser and synchrotron radiation—The nf′ Rydberg states of neon

A mode-locked tunable Ti:Sapphire oscillator has been synchronized with the time structure of a storage ring and used to study the photoionization of noble gases. In multi-bunch operation of the ring the setup permits the observation of the dynamics from a few nanoseconds down to the tens of picoseconds range. The characteristics of the setup are demonstrated by following the two-color ionization of helium (via the 1s3p 1P o state) and argon (via the 3p 5 ( 2P 3/2) 3d state). In the CW mode we have also examined the two-color ionization of neon via the 2p 5 ( 2P 1/2) 3d′ state. In neon the nf′ Rydberg series was followed up to n∼50, and the quantum defect was determined.

Theoretical interpretation of multiphoton ionization of neon by soft-x-ray intense radiation

We present an attempt at the theoretical interpretation of recent experimental results on multiphoton ionization of neon by photons of energies 38.4 and 42.8 eV at the free electron laser facility [A. A. Sorokin et al., Phys. Rev. A 75, 051402(R) (2007)]. Although, given the photon energies, the intensities employed place the process within the regime of perturbation theory, effects such as the pulsed nature of the field and expansion of the interaction volume need to be and are taken into consideration. The values of some of the cross sections are obtained through scaling and given the semiquantitative nature of the calculations, overall reasonable agreement with the experimental data is found, although some issues pertaining to details remain as questions.

Angular differential cross sections for multiple ionization of rare gas atoms by protons with inclusion of Auger-like processes

Based on the independent particle model, we consider single and multiple ionization of neon and argon atoms induced by fast proton impact. Multiple ionization at high projectile energies (EP ⪆ 1 MeV/amu) is dominated by Auger-like processes and can be described appropriately by our statistical model introduced recently. In the present work we use several scattering models to extract angular differential cross sections. With our results a long-standing discrepancy between different experimental data sets is resolved.

Towards non-sequential double ionization of Ne and Ar using a femtosecond laser oscillator

We report on first proof-of-principles results on non-sequential double ionization of argon and neon achieved by using a newly developed long-cavity Ti:sapphire femtosecond oscillator with a pulse duration of 45 fs and a repetition of 6.2 MHz combined with a dedicated reaction microscope. Under optimized experimental conditions, peak intensities larger than 2.310(14) W/cm(2) have been achieved. Ion momentum distributions were recorded for both rare gases and show significantly different features for single as well as for double ionization. For single ionization of neon a spike of zero-momentum electrons is found when decreasing the laser intensity towards the lowest ionization rate we can measure which is attributed to a non-resonant ionization channel. As to double ionization, the longitudinal momentum distribution for Ne(2+) displays a clear double-hump structure whereas this feature is found to be smoothened out with a maximum at zero momentum for Ar(2+).

High‐Resolution X‐Ray Spectroscopy of the Interstellar Medium. II. Neon and Iron Absorption Edges

We present high-resolution spectroscopy of the neon K-shell and iron L-shell interstellar absorption edges in nine X-ray binaries using the High Energy Transmission Grating Spectrometer (HETGS) on board the Chandra X-Ray Observatory. We found that the iron absorption is well fit by an experimental determination of the cross section for metallic iron, although with a slight wavelength shift of ≈20 mA. The neon edge region is best fit by a model that includes the neutral neon edge and three Gaussian absorption lines. We identify these lines as due to the 1s-2p transitions from Ne II, Ne III, and Ne IX. As we found in our oxygen edge study, the theoretical predictions for neutral and low-ionization lines all require shifts of ≈20 mA to match our data. Combined with our earlier oxygen edge study, we find that a best-fit O/Ne ratio of 5.4 ± 1.6, consistent with standard interstellar abundances. Our best-fit Fe/Ne ratio of 0.20 ± 0.03 is significantly lower than the interstellar value. We attribute this difference to iron depletion into dust grains in the interstellar medium. We make the first measurement of the neon ionization fraction in the ISM. We find Ne /Ne ≈ 0.3 and Ne /Ne ≈ 0.07. These values are larger than is expected given the measured ionization of interstellar helium. For Ne IX, our results confirm the detection of the hot ionized interstellar medium of the Galaxy.

Fully differential rates for femtosecond multiphoton double ionization of neon.

We have investigated the full three-dimensional momentum correlation between the electrons emitted from strong field double ionization of neon when the recollision energy of the first electron is on the order of the ionization potential. The momentum correlation in the direction perpendicular to the laser field depends on the time difference of the two electrons leaving the ion. Our results are consistent with double ionization proceeding through transient double excited states that field ionize.

Multielectron ionization processes in ultrastrong laser fields

The ionization of neon was studied in strong (1014–1016 W/cm2) and ultrastrong (1017–1018 W/cm2) laser fields. Measurements of ionization yields in ultrastrong fields reveal that they are dominated by sequential tunneling ionization of the ion charge states. The rescattering mechanism, identified with the generation of high-order harmonics and multiple electron ionization in strong fields, is modeled for ultrastrong fields and is shown to be reduced by orders of magnitude when compared with strong-field ionization. The results from the model are consistent with the experimental results and indicate that the reduced core size for ions and the Lorentz force in ultrastrong fields combine to reduce rescattering in ultrastrong fields.

Post-collisional effects in multiple ionization of neon by protons

Absolute cross sections for single and multiple ionization of Ne by fast(0.75–3.50 MeV) protons have been measured. The comparison with availabletheoretical calculations shows that the inclusion of the contribution fromtime-delayed post-collisional mechanisms is needed for a good description of theexperimental results for double and triple ionization at high velocities.

Doubly differential electron-emission spectra in single and multiple ionization of noble-gas atoms by fast highly-charged-ion impact

Low-energy electron emission spectra are studied in collisions of 3.6 MeV/amu ${\mathrm{Au}}^{53+}$ ions with neon and argon atoms for well-defined degrees of target ionization. We calculate doubly differential cross sections as functions of the recoil-ion charge state in the continuum-distorted-wave with eikonal initial-state approximation using a binomial analysis of the total and differential ionization probabilities, and compare them with the present and with previously published experimental data. Very good agreement is found for the single-ionization spectra and for double ionization of neon, while some discrepancies are observed in the spectra for double and triple ionization of argon.

Two-dimensional MHD simulations of a neon Z pinch on Hawk

Two-dimensional magnetohydrodynamic (MHD) simulations using MACH2 are benchmarked against laser shearing interferometer (LSI) images of the evolving electron-density sheath during 250-ns neon gas-puff Z pinch implosions on the Naval Research Laboratory Hawk generator. The initial density distribution for the MHD simulations is calculated using a ballistic-flow-model fit to the measured initial gas-density distributions. The implosion is modeled using an applied current profile, single-temperature energy equations, and black-body-limited optically thin radiation. For consistency with the radiation model, neon ionization and equation-of-state models have been added to MACH2. Computed MHD ion-density distributions compare well with LSI images as the snowplowed plasma channel evolves during implosion. The MHD results also show features that may be helpful for understanding early and weak K-shell radiation observed near the nozzle in Double-Eagle gas-puff experiments. Current-channel evolution derived from one-dimensional snowplow calculations compare well to the MHD results for the same current history and initial density distribution, indicating that axial mass flow does not strongly impact the implosion dynamics.

Electron-electron correlation in laser-induced nonsequential double ionization

The distributions of the momenta of the two electrons liberated in nonsequential double ionization of neon and argon are calculated in the S-matrix formalism assuming a rescattering scenario. Two different forms for the electron-electron correlation are compared: the Coulomb repulsion in the Born approximation and a three-body contact interaction including the ion. The former favors disparate momenta of the two electrons, the latter equal momenta.