A model of a two-electron mechanism of formation of doubly charged ions upon multiphoton ionization of alkaline-earth atoms

A model of a two-electron mechanism of formation of doubly charged ions upon multiphoton ionization of alkaline-earth atoms is described on the basis of recent experimental studies.     

Two-photon excitation/ionization of deep shells of multiply charged atomic ions

Absolute values and the shape of cross sections for two-photon one-electron excitation/ionization of the 1s shell of Ne⁶⁺ and Ne⁸⁺ ions, taking into account the relaxation of the atomic core in the field of resulting vacancies, are calculated. The many-particle stabilization of a deep vacancy in moving from a neutral atom to multiply charged ions is taken into account. The calculations are made for linear and circular polarizations of the incident laser beam. The results of the calculations are predictive.     

Comparison study of atomic and molecular single ionization in the multiphoton ionization regime

In this Letter, we report, for the first time in the multiphoton ionization regime, a comparison study of single-electron ionization of diatomic molecules versus rare gas atoms with virtually the same ionization potentials. In comparing N2+ to Ar+, a higher ion signal is seen in N2+ compared to Ar+ for linear polarization but the difference vanishes in circularly polarized light. In comparing O2+ to Xe+, we observe a suppression in O2+ compared to Xe+ for both linear and circular polarization but this suppression exhibits an intensity dependence; i.e., there is little suppression for O2+ at the lowest intensity range, but the suppression becomes increasingly stronger as the laser intensity increases. The multielectron screening model is used to discuss possible mechanisms of this intensity dependent suppression in O2+ in the multiphoton ionization regime.     

Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H⁺, He²⁺, Li2,3+, C2,3,4,5,6+, N2,3,4,5+, O2,3,4,5,6+, and Ar3,4,5,6+ ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.     

碘原子共振多光子电离光谱研究

用可调谐的染料激光(4600～5000(?)),共振(3+2)和(4+1)多光子电离探测了I(5p~2P_(3/2)~0)和1~#(5p~2P_(1/2)~0).碘原子是由碘分子(I_2)经激光解离而产生的.在上述激光波段中共观察到12个原子跃迁,其中,(4+1)多光子电离跃迁是首次观察到的.     

On the infinite summation in the theory of atomic multiphoton ionization

The infinite summation through the complete set of real unperturbed atomic states that appears in the Nth-order time-dependent perturbation theory when applied to multiphoton ionization is calculated by using the Green's function method. The cross-sections so obtained are in good agreement with other theoretical values published elsewhere.     

Resonant structure of the formation of doubly charged ions in multiphoton ionization of Sr atoms in the infrared spectral region

The process of forming doubly charged ions in ionization of Sr atoms by laser radiation in the frequency region of 8200–9100 cm^?1 is studied experimentally. The resonant structure of the yield of these ions as a function of the radiation frequency is found to be determined by the excitation of strongly perturbed states of Sr atoms.     

Cross sections for single and double ionization of atomic helium under impact by fast multiply charged ions

Expressions for the cross sections for single and double ionization of atomic helium in collisions with fast multiply charged ions are obtained in the collision parameter range υ ²≫Z≳υ, υ ₀<c, where Z and υ are, respectively, the ion charge and ion velocity, υ ₀ is the characteristic velocity of electrons in the atomic helium ground state, and c is the velocity of light. Zh. Tekh. Fiz. 68, 1–7 (March 1998)     

Relativistic calculations of electron-impact ionization for highly charged hydrogen-like ions

Electron-impact ionization cross-sections and rate coefficients of the 1s ground state for H-like C, O, Mg, Ar, Fe, Cu, As, Kr, Y, Mo ions with incident electron energies up to 15 times the ionization threshold energy have been systematically calculated by the relativistic distorted-wave Born exchange (DWBE) approximation. The comparison of the result with the experimental data, other theoretical calculations and recommended values shows the very good agreement. The influence from relativistic and the lowest order QED effect in the calculation is discussed. The calculated ionization cross-sections are fitted by empirical formulas. These fits can be readily integrated over a relativistic Maxwellian electron distribution function to obtain rate coefficient for plasma modeling.     

Electron capture by slow multiply charged Ar and Ne ions from atomic hydrogen

At collision energies below 15 keV total charge transfer cross sections have been measured for multiply charged Ar^ζ+(2≦ζ≦6) and Ne^ζ+(2≦ζ≦4) ions colliding with atomic hydrogen. A Wood discharge was used to provide a hydrogen target with a sufficiently high degree of dissociation. Results are compared with measurements performed at higher energies and with theoretical calculations. For ζ=2 cross sections in atomic hydrogen are much smaller than in the molecular case, for ζ>2 the ratio of these cross sections varies between 0.7 and 1.6.     

Highly charged ions in field evaporating 4d-transition metals

An energy-focused time-of-flight atom-probe has been employed in a search for high ionic charges obtained in field-evaporating Zr, Nb, Mo, Rh, Pd and Ag, the 4d-transition metals. Although no new higher charges than the already established ones are found for these metals the maximum abundance of the highest charge is determined in each case. An empirical rule predicting the limits of the charge of field-evaporating ions is proposed.     

Highly charged ions from laser-cluster interactions: local-field-enhanced impact ionization and frustrated electron-ion recombination

Our molecular dynamics analysis of Xe_{147-5083} clusters identifies two mechanisms that contribute to the yet unexplained observation of extremely highly charged ions in intense laser cluster experiments. First, electron impact ionization is enhanced by the local cluster electric field, increasing the highest charge states by up to 40%; a corresponding theoretical method is developed. Second, electron-ion recombination after the laser pulse is frustrated by acceleration electric fields typically used in ion detectors. This increases the highest charge states by up to 90%, as compared to the usual assumption of total recombination of all cluster-bound electrons. Both effects together augment the highest charge states by up to 120%, in reasonable agreement with experiments.     

Deep-core dielectronic-capture resonances in the electron-impact ionization of heavy atomic ions

Experimental measurements and theoretical calculations are carried out for the electron-impact ionization of Sm(12+). The low energy region of the single ionization cross section for Sm(12+) is found to be dominated by contributions from the indirect process of excitation autoionization. At about 1.0 keV strong resonance features are found in the experimental crossed-beam measurements performed in scan mode at high resolution. Theoretical calculations confirm that the high energy experimental features are due to deep-core dielectronic capture followed by sequential double Auger decay. The discovery of these unusual high energy resonances in single and multiple ionization opens the door for future systematic studies of how heavy atomic ions with deep inner-shell vacancies achieve final stabilization.