Total Autoionization Research Articles

Triple autoionization of atomic ions

A time-dependent close-coupling method for four-electron atomic systems is formulated to calculate the triple autoionization of atomic ions. Initial excited states are obtained by relaxation of the Schrodinger equation in imaginary time using a Schmidt orthogonalization method involving interior subshells. Autoionization rates are obtained by propagation in real time using projections onto products of bound and continuum single particle states. For the () excited configuration of the atomic ion, we obtain total, double, and triple autoionization rates. The total autoionization rates are in reasonable agreement with single autoionization rates obtained using configuration-average distorted-wave theory.

Photoionization using the xchem approach: Total and partial cross sections of Ne and resonance parameters above the 2s22p5 threshold

The XCHEM approach interfaces well established quantum chemistry packages with scattering numerical methods in order to describe single-ionization processes in atoms and molecules. This should allow one to describe electron correlation in the continuum at the same level of accuracy as quantum chemistry methods do for bound states. Here we have applied this method to study multichannel photoionization of Ne in the vicinity of the autoionizing states lying between the $2{s}^{2}2{p}^{5}$ and $2s2{p}^{6}$ ionization thresholds. The calculated total photoionization cross sections are in very good agreement with the absolute measurement of Samson et al. [J. Electron Spectrosc. Relat. Phenom. 123, 265 (2002)], and with independent benchmark calculations performed at the same level of theory. From these cross sections, we have extracted resonance positions, total autoionization widths, Fano profile parameters, and correlation parameters for the lowest three autoionizing states. The values of these parameters are in good agreement with those reported in earlier theoretical and experimental work. We have also evaluated $\ensuremath{\beta}$ asymmetry parameter and partial photoionization cross sections and, from the latter, partial autoionization widths and Starace parameters for the same resonances, not yet available in the literature. Resonant features in the calculated $\ensuremath{\beta}$ parameter are in good agreement with the experimental observations. We have found that the three lowest resonances preferentially decay into the $2{p}^{\ensuremath{-}1}\ensuremath{\epsilon}d$ continuum rather than into the $2{p}^{\ensuremath{-}1}\ensuremath{\epsilon}s$ one [Phys. Rev. A 89, 043415 (2014)], in agreement with previous expectations, and that in the vicinity of the resonances the partial $2{p}^{\ensuremath{-}1}\ensuremath{\epsilon}s$ cross section can be larger than the $2{p}^{\ensuremath{-}1}\ensuremath{\epsilon}d$ one, in contrast with the accepted idea that the latter should amply dominate in the whole energy range. These results show the potential of the XCHEM approach to describe highly correlated process in the ionization continuum of many-electron systems, in particular molecules, for which the XCHEM code has been specifically designed.

Autoionization widths of open-M-shell germanium ions: effects on inner-shell absorptions

Large-scale configuration interaction calculations were carried out to obtain the level-by-level autoionization (AI) rates and resonance widths of the inner-shell excited configurations for the open-M-shell germanium ions. Detailed results are presented for Ge5+ as an example. The dominant ionization channels of the autoionized levels 2p53/23s23p63d10 and 2p51/23s23p63d10 of Ge5+ were determined, and it is shown that the channel from level 3s23p6(3d−13/23d−15/2)4 contributes the largest fraction of AI widths of 0.195 and 0.188 eV to the total width of 0.577 and 0.544 eV, respectively, from all possible channels. For typical experimental plasmas at temperatures of several tens and hundreds of eV, the AI resonance broadening is the dominant mechanism among the Doppler, electron impact and natural lifetime broadenings. Among the physical effects such as relativistic and the interaction between fine-structure levels belonging to the same non-relativistic configuration and different configurations, particular attention is paid to the effect of AI resonance broadening on the L-shell absorption. Different features of the inner-shell absorption due to AI broadening are presented in detail for Ge5+, Ge10+ and Ge17+. The total AI widths of levels from the configuration of one 2p electron being excited to 3d orbital were systematically investigated for Ge6+–Ge21+. Except for Ge20+ and Ge21+, the AI widths of the open-M-shell germanium ions dominate over all other line broadening mechanisms.

Partial widths with interchannel coupling for the3PoWannier-ridge states ofH−

We have computed the partial and total autoionization widths with interchannel coupling for the ${}^{3}{P}^{o}$ Wannier-ridge resonances of ${\mathrm{H}}^{\ensuremath{-}}$ below the $n=3$, 4, 5, 6, and 7 hydrogenic thresholds. The complex eigenvalue Schr\"odinger equations are solved using square-integrable wave functions with numerical and analytic real and complex orbitals. Trends regarding the decay dynamics and the excitation of high-orbital-angular-momentum electrons near threshold are established.

Resonance excitation of the 3p 6-subshell in potassium: Contribution to the single ionization

The total autoionization cross-section of potassium has been studied as a function of incident electron energy over the range from the lowest autoionization threshold at 18.72 eV to 24.4 eV and at an energy resolution of 0.25 eV. The cross-section has been obtained by determining the normalized total intensities of ejected-electron spectra accurately measured at the magic angle of 54.7°. The structure observed in the autoionization function has been assigned to the negative-ion resonances based upon the lowest autoionizing configurations 3p 54s 2 and 3p 53d4s. The quartet levels from the 3p 53d4s configuration give the bulk of the autoionization contribution in the single ionization cross-section in the energy range 20.5–24.4 eV. Comparison of the present results with earlier available experimental and theoretical results is presented.

Electron impact double ionization of krypton ions (q = 14-17)

Absolute cross sections for electron impact double ionization ofkrypton ions Krq + (q = 14-17) have been measuredfrom threshold to 5 keV. The animated crossed beam method has been employed. Direct double ionization is seen to reducestrongly along the isonuclear sequence.Ionization-autoionization from the inner L-shell is seen to bethe dominant process. It is roughly approximated by thesemi-empirical Lotz formula assuming total autoionization ofthe ionic intermediate states. Resonant capture and excitationprocesses implying the L-shell are also obtained for chargestates 14-16.

Electron Impact Ionization of Nickel Multiply-Charged Ions

Absolute cross-section measurements are reported for electron impact ionization of Ni12+ and Ni14+ in an energy range from threshold to about 5.5 keV. For single ionization, data show that the first observed threshold corresponds to the metastable state [Ne]3s23p4 1S0 which is located 12 eV above the ground state. Excitation-autoionization is seen to play a dominant role for this reaction in the whole energy range. Double ionization is seen to be dominated by L-shell ionization followed by total autoionization. For Ni12+, triple ionization is found to be two orders of magnitude lower than double ionization and is attributed to direct ionization only.

Comparison of the Total Autoionization Rates for1s2s22p2, 1s2s2p3, 1s2p4States of B-like Ions (6 ≤ Z ≤ 54)

Comparison of three different calculational methods MZ, AUTOLSJ,and MCDF have been done for autoionization rates of doubly excitedstates 1s2s22p2, 1s2s2p3,1s2p4 of B-like ions in a wide range of nuclear charge Z (6 ≤ Z ≤ 54).

Autoionization rates for 1s2s22p2,1s2s2p3, 1s2p4 states of B-like ions(6 < Z < 54) for decay via different channels

Two different calculational methods, MZ and AUTOLSJ, are used toobtain autoionization rates for doubly excited states1s2s22p2,1s2s2p3, 1s2p4of B-like ions in a wide range of nuclear charge Z (6 ⩽ Z ⩽ 54). Besides the total autoionization ratesdecayed via channels, so-called partial rates are computed in theintermediate coupling scheme. The Z-dependences of thepartial rates are investigated in detail. A comparison shows a goodagreement between these two methods. These data can be used to modeldielectronic satellite spectra in plasmas. In particular, amplitudesand partial rates of autoionization decay are of importance fordetailed atomic kinetic calculations and for the the study ofpolarization properties of dielectronic satellitespectra.

Angle-differential electron energy spectra for the autoionization systems He∗ (2 1S) + H/D(1 2S): Comparison between ab initio theory and experiment

We present angle-dependent electron energy spectra due to ionizing collisions ofmetastable He∗ (2 1S) atoms with ground-state hydrogen and deuterium atoms. The data, measured at thermal collision energies (Ērel≈50 meV), show an angular variation of the spectral shape which is well reproduced by a quantum-mechanical calculation based on local complex potential theory. The ab initio calculated resonance-to-continuum complex coupling elements show a strong dependence on the electronic structure of the quasi-molecule and its changes with internuclear separation. Therefore the total autoionization width shows a significant deviation from a damped exponential shape. Autoionization occurs dominantly into the (molecule fixed) electronic p wave. Calculated total autoionization cross sections are 84 Å2 at Erel = 50 meV. and follow approximately a Erel−0.5 decay for larger energies. At Erel = 50 meV, associative and quasi-associative processes account for about 12% and 4%, respectively, of the total cross section.

Effect of interchannel coupling on the partial and total autoionization widths: Application to the 1s3s3p 4Po and 1s3p2 4P states for Z=2-5, 10.

We have computed the partial and total widths with interchannel coupling for the 1s3s3p $^{4}$${\mathit{P}}^{\mathit{o}}$ and 1s3${\mathit{p}}^{2}$ $^{4}$P states for Z=2--5 and 10, by solving the corresponding complex matrix equations constructed from square-integrable N-electron functions with numerical and analytic real and complex orbitals. The correlated wave functions are computed by the state-specific method. Oscillator strengths for one- and two-electron transitions from the metastable 1s2s2p $^{4}$${\mathit{P}}^{\mathit{o}}$ state suggest that the states are reachable in ${\mathrm{He}}^{\mathrm{\ensuremath{-}}}$ and in Li directly, (1s3${\mathit{p}}^{2}$ $^{4}$P), or via the 1s2${\mathit{p}}^{2}$ $^{4}$P state (1s3s3p $^{4}$${\mathit{P}}^{\mathit{o}}$). The effect of interchannel coupling on the partial widths in the case of the $^{4}$${\mathit{P}}^{\mathit{o}}$ state is considerable. On the contrary, interchannel coupling has no significant effect on the total widths. This computational result is discussed formally.

Partial autoionization rates of O4+ (1s2s22p)3P0 and 1P0: A crucial test of electron correlation in Be-like systems.

For the first time, ratios of partial autoionization widths have been measured for highly ionized oxygen projectiles. In particular we have studied the Auger decay of the Be-like (1s2${s}^{2}$2p${)}^{3}$${P}^{0}$ and $^{1}\mathrm{P}^{0}$ states in ${0}^{4+}$ decaying to the 1${s}^{2}$2p and 1${s}^{2}$2s final ionic states. Our experimental intensity ratios for the $^{3}\mathrm{P}^{0}$ and $^{1}\mathrm{P}^{0}$ states are 1.7 and 16, respectively. We also present new results on the partial and total autoionization widths of these states from calculations which include electron correlation and interchannel coupling via the application of the many-electron theory of ionic resonances in terms of complex coordinates.

Energy and angular distributions of electrons ejected from theBa (6pjns12)1states

We describe the energy and angular distributions of electrons ejected from the $\mathrm{Ba} {(6{p}_{j}n{s}_{\frac{1}{2}})}_{1}$ states in their autoionization to the ${\mathrm{Ba}}^{+} 6s$, $5d$, and $6p$ states. The atoms are excited by a three-step laser approach which enables us to excite to the autoionizing state from the spherically symmetric $6sns ^{1}S_{0}$ states. Since we excite to the discrete part of an autoionizing state, the angular distributions are different from those expected for continuum excitation. Both the angular distributions of the ejected electrons and branching ratios to the available ion states exhibit much more variation than would have been anticipated on the basis of the ${n}^{\ensuremath{-}3}$ dependence of the total autoionization rates.

Two-photon autoionization of H 2

We present a model calculation for two-photon autoionization to the X 1Σ g state of H + 2. We calculate the total autoionization cross section and the line shape including the effect of laser intensity.

Dynamic Coupling Phenomena in Molecular Excited States. II. Autoionization and Predissociation inH2, Hd, andD2

Vibrationally induced autoionization and one class of predissociation of electronically excited ${\mathrm{H}}_{2}$ and its isotopes are treated by a perturbed-stationary-state theory. Autoionization and predissociation rates are given for a number of states of ${\mathrm{H}}_{2}$, HD, and ${\mathrm{D}}_{2}$. In addition to direct bound-continuum coupling, consideration is given to effects of higher-order coupling; these effects cause order-of-magnitude changes in isolated cases. The auto-ionization rates vary with principal quantum number $n$ as ${n}^{\ensuremath{-}3}$, directly with vibrational energy $\mathrm{vh}\ensuremath{\nu}$, and decrease sharply with vibrational quantum change $\ensuremath{\Delta}v$. As the principal quantum number increases, transitions of successively smaller $\ensuremath{\Delta}v$ become possible; the net effect of this is to override the ${n}^{\ensuremath{-}3}$ dependence in total autoionization rates. Competition between predissociation and autoionization is examined; the two processes show very different dependence on $n$ and $v$, with the consequence that decay in most regions of ($n, v$) space is dominated by one or the other process; but the two mechanisms are competitive for some ($n, v$) states. The isotope effect also is rather different for the two decay processes, enough so that, in effect, the isotope effect amounts to a qualitative change from one mechanism of decay to the other, with mass change.