Spectroscopy and metastability of CO22+ molecular ions

The spectroscopy and metastability of the carbon dioxide doubly charged ion, the CO22+ dication, have been studied with photoionization experiments: time-of-flight photoelectron photoelectron coincidence (TOF-PEPECO), threshold photoelectrons coincidence (TPEsCO), and threshold photoelectrons and ion coincidence (TPEsCO ion coincidence) spectroscopies. Vibrational structure is observed in TOF-PEPECO and TPEsCO spectra of the ground and first two excited states. The vibrational structure is dominated by the symmetric stretch except in the TPEsCO spectrum of the ground state where an antisymmetric stretch progression is observed. All three vibrational frequencies are deduced for the ground state and symmetric stretch and bending frequencies are deduced for the first two excited states. Some vibrational structure of higher electronic states is also observed. The threshold for double ionization of carbon dioxide is reported as 37.340+/-0.010 eV. The fragmentation of energy selected CO22+ ions has been investigated with TPEsCO ion coincidence spectroscopy. A band of metastable states from similar to38.7 to similar to41 eV above the ground state of neutral CO2 has been observed in the experimental time window of similar to0.1-2.3 mus with a tendency towards shorter lifetimes at higher energies. It is proposed that the metastability is due to slow spin forbidden conversion from bound excited singlet states to unbound continuum states of the triplet ground state. Another result of this investigation is the observation of CO++O+ formation in indirect dissociative double photoionization below the threshold for formation of CO22+. The threshold for CO++O+ formation is found to be 35.56+/-0.10 eV or lower, which is more than 2 eV lower than previous measurements. (C) 2005 American Institute of Physics.

Equilibrium structure of erbium-oxygen complexes in crystalline silicon

The equilibrium structure of ErOn (nless than or equal to6) complexes in crystalline silicon has been investigated by density-functional computations. Two different geometries have been considered, corresponding to the substitutional and tetrahedral interstitial site for erbium. All atomic coordinates have been optimized by Car-Parrinello molecular dynamics. The resulting structures have low symmetry, with E-O distances of similar to2.35 Angstrom. The substitutional site is the most stable one for nless than or equal to2, while the tetrahedral interstitial is favored for n>2.

Electron impact ionization of hydrogen-like molybdenum ions

The electron impact ionization cross sections of hydrogen-like molybdenum ions were measured with an electron beam ion trap at the electron energies of 49.4, 64.4 and 79.6 keV The results are 2.82(22) x 10(-23), 3.13(29) x 10(-23) and 3.23(51) x 10(-23) cm(2), respectively. These results are compared with the experimental results measured previously. The agreement with the results obtained with, scaling formulae is also discussed.

Electron-impact ionization of hydrogen-like iron ions

Electron-impact ionization cross sections have been determined for hydrogen like iron ions at selected electron energies between 1.45 and 4.3 times the threshold energy. The cross sections were obtained by measuring the equilibrium ionization balance in an electron beam ion trap. This ionization balance is obtained from x-ray measurements of radiative recombination into the K-shell of hydrogen-like and bare iron ions. The measured cross sections are compared with distorted-wave calculations and several semiempirical formulations.

The measurement of the dielectronic recombination in He-like Fe ions

We have studied the dielectronic recombination process in He-like Fe ions and have obtained the resonant strengths of the KLn (3 less than or equal to, n less than or equal to, 5) resonances. This measurement was performed with the use of an electron beam ion trap by measuring the x-ray energy emitted from highly charged ions simultaneously with the electron beam energy scanned during the measurement. The total resonant strengths obtained are 5.0 x 10(-19), 2.1 x 10(-19) and 1.1 X 10(-19) cm(2) eV, for KLM, KLN and KLO, respectively.

Measurements of temperature dynamics of ions trapped inside an electron beam ion trap and evidence for ionisation heating

A technique is described whereby measurements of ions extracted from an electron beam ion trap can be used to deduce their temperature dynamics. The measured temperature dynamics shows the expected trend as a function of charge and also gives evidence for Landau-Spitzer heating, ionization heating and evaporative cooling.

Parity nonconservation in electron recombination of multiply charged ions

We discuss a parity nonconserving asymmetry in the cross section of KLL dielectronic recombination of polarized electrons on the hydrogenlike ions with Z less than or similar to 60. This effect is strongly enhanced because of the near degeneracy of doubly excited 2l2l(') states of opposite parity in He-like ions. For ions with Z similar to 30 the asymmetry is of the order of 10(-9). For Z approximate to 48 a level crossing takes place, leading to the PNC asymmetry of -1.3x10(-8), which is 10(8) times greater than the basic strength of the weak interaction in atoms.

Electron spectroscopy of doubly excited states in He produced by slow collisions of He2+ ions with Ba atoms

We measured ejected electron spectra caused by autoionization of doubly excited states in He atoms; the excited He was made by double electron capture of low-energy He2+ ions colliding with Ba atoms. Measurements were performed by means of zero degree electron spectroscopy at projectile energies from 40 to 20 keV. Electron spectra due to autoionization from the states He(2lnl') to He+(1s) for n greater than or equal to2, and those from He(3lnl') to He+ (2s or 2p) for n greater than or equal to3, were observed. Line peaks in the spectra were identified by comparing observed electron spectra with those of several theoretical calculations. It was found that doubly excited states of relatively high angular momenta such as the D and F terms were conspicuously created in a quite different manner from the cases of the production of doubly excited states by the use of photon, electron, or ion impacts on neutral He atoms. Rydberg states with large n values were observed with high population in both the He(2lnl') and He(3lnl') series. Other remarkable features in the electron spectra are described and the mechanisms for the production of these electron spectra are discussed qualitatively.

Dielectronic recombination in highly charged He-like ions

We have determined resonant strengths of the KLn (2 less than or equal to n less than or equal to 5) resonances for helium-like Ti ions and (3 less than or equal to n less than or equal to 5) resonances for helium-like Fe ions. The results were obtained using the Tokyo electron beam ion trap. Characteristic X-rays from both dielectronic recombination and radiative recombination were detected as the electron beam energy was scanned through the resonances. (C) 2003 Elsevier Science B.V. All rights reserved.

Dielectronic recombination in He-like titanium ions

Dielectronic recombination (DR) has been studied in highly charged He-like Ti ions using an electron beam ion trap. X-rays emitted from radiative recombination (RR) and DR were observed as the electron beam energy was scanned through the resonances. Differential DR resonant strengths were determined by normalizing the DR x-ray intensity to the RR intensity using theoretical RR cross sections. KLn (2 less than or equal to n less than or equal to 5) resonant strengths were determined for He-like Ti ions. The differential resonant strengths were calibrated without reference to any theoretical DR calculations while the electron energy scale was derived with reference to the well-known energy for ionization of the He-like and H-like ions from the ground state. Calibration in this way facilitates a more exacting comparison between theory and experiment than has been reported previously. To facilitate this comparison, total and differential theoretical resonance strengths were calculated. These calculations were found to be in good agreement with the measured results.

Systematic study of visible transitions in Ti-like high Z ions

The magnetic dipole transitions between fine structure levels in the ground term of Ti-like ions, (3d(4)) D-5(2)-D-5(3), were investigated by observation of visible and near-UV light for several elements with atomic numbers from 51 to 78. The wavelengths are compared with theoretical values we recently calculated. The differences between the present calculations and measurements are less than 0.6%. The anomalous wavelength stability predicted by Feldman, Indelicato and Sugar [J. Opt. Soc. Am. B 8, 3 (1991)] was observed. We attribute this anomalous wavelength stability to the transition from LS to JJ coupling and the asymptotic behavior of the transition energies in the intermediate coupling regime.

The measurement of the electron impact ionization cross-sections of hydrogen-like ions

We have measured electron impact ionization cross-sections of hydrogen-like iron and hydrogen-like molybdenum with an electron beam ion trap. The measurements were performed in the electron energy range between 13.5 and 40 keV for hydrogen-like iron and between 50 and 80 keV for hydrogen-like molybdenum. (C) 2003 Elsevier Science B.V. All rights reserved.

Dielectronic recombination of hydrogen-like ions

Decay dynamics of dielectronic recombination (DR) processes of H-like titanium ions was investigated with an electron beam ion trap. In the DR of H-like ions a K-shell vacancy is available even after the decay of the doubly excited state produced by the recombination. Therefore secondary X-ray emission is possible. An observed X-ray spectrum of DR obtained in the present experiment was well reproduced theoretically by taking into account the secondary X-rays. (c) 2005 Elsevier B.V. All rights reserved.