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Ejected electron spectra from the singlet and triplet states of doubly excited Ne6+**(1s22pnl), Ne6+**(1s23l3l') and Ne6+**(1s23l4l') ions, produced by 80 keV Ne8+(1s2) + He, Ne and Ar collisions, have been measured by means of a zero-degree electron spectroscopy. Only singlet states were observed when the target was He. In contrast, the contribution from the triplet states prevailed in the spectra for the Ne target. For the Ar target, practically no signals were observed in the energy region for the 1s23lnl' states. Two theoretical methods, the perturbation theory (MZ code) and the multi-configurational Hartree-Fock (Cowan code) were used for identification of ejected-electron spectra. Using the (j) string analysis in the extended classical over-barrier model, we discuss the possibility of the participation of inner electrons in the process of double-electron capture by highly charged ion multi-electron target atoms.

Polarization of the radiation from Zn and Cd atoms (n = 4 for Zn and 5 for Cd, respectively) was observed after electron impact with energy slightly above the threshold excitation energy. The observing direction was perpendicular to both the incident electron beam and the atomic beam. All of the triplet radiation (J = 0, 1 and 2) was slightly polarized. The observed fractional polarization degrees were and corresponding to J = 0, 1 and 2 spectra in the final states of the Zn atom and , 4.3 and for the Cd atom. These values could be explained by assuming populations in the sublevels and of the states deviating from an equal mean value of for each sublevel. It is interesting and reasonable that the deviations determined independently for different states coincided with each other quite well. The deviated values of fractional population for the sublevel were 0.36 for Zn and 0.37 for Cd, respectively.

Ejected electrons from the singlet and triplet states of doubly excited and ions, produced by 25, 50, 75 and 100 keV and Ar collisions have been measured with high-resolution electron spectroscopy. Only singlet states were observed when the target was He; in contrast, many triplet states were observed in and Ar collisions. Both singlet and triplet states contributed to the electron spectra in collisions, in particular, triplet states were conspicuous at low energy. Two theoretical methods, perturbation theory or Z expansion (MZ code) and multiconfigurational Hartree-Fock (Cowan code) were used for identification of ejected-electron spectra. The collision energy dependence of the spectra is discussed.

Differential cross sections (DCS's) for excitation of the $2{}^{1}S$ and $3{}^{1}S$ states in helium have been measured at small scattering angles from 0\ifmmode^\circ\else\textdegree\fi{} to 15\ifmmode^\circ\else\textdegree\fi{} for the electron-impact energies from 100 to 500 eV. Measurements were performed with a high angular resolution, better than 1\ifmmode^\circ\else\textdegree\fi{}, and with an accuracy of the angle position of 0.2\ifmmode^\circ\else\textdegree\fi{}. Distinct forward peaking features have been observed at minute scattering angles lower than about 3\ifmmode^\circ\else\textdegree\fi{} for impact energies higher than 200 eV. Experimental DCS's as functions of the scattering angle are compared with theoretical calculations based on various kinds of approximation method. Effective generalized oscillator strengths (GOS's) for the $2{}^{1}S$ and $3{}^{1}S$ excitations were deduced from the DCS's for impact energies 100--500 eV as a function of the squared momentum transfer ${K}^{2}.$ A systematic discrepancy between the measured effective GOS's and the theoretical GOS calculated by the first Born approximation has been displayed at the low limit of ${K}^{2}.$ The effective GOS's appear to approach the theoretical GOS very slowly as the impact energy increases, however, the GOS for low values of ${K}^{2}$ still does not agree with the theoretical GOS up to the impact energy 800 eV for the $2{}^{1}S$ excitation.

Differential cross sections and generalized oscillator strengths have been measured for two optically allowed transitions 5${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)5d(K=3/2,J=1) and 5${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)7s(K=3/2,J=1) and two optically forbidden transitions 5${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)5d(K=7/2,J=3) and 5${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)5d(K=5/2, J=3) in Xe by means of electron-energy-loss spectroscopy. These measurements are carried out for electron kinetic energies of 400 and 500 eV at small scattering angles (\ensuremath{\theta}=1.4\ifmmode^\circ\else\textdegree\fi{}--15.1\ifmmode^\circ\else\textdegree\fi{}). Optical oscillator strengths have been determined by extrapolating the generalized oscillator strengths to zero momentum transfer, as (0.298\ifmmode\pm\else\textpm\fi{}0.045) and (0.0738\ifmmode\pm\else\textpm\fi{}0.011), for the 5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)5d(K=3/2,J=1) and 5${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)7s(K=3/2,J=1) states, respectively. Integrated cross sections have also been determined for each impact energy. The errors are estimated to be less than 15%. \textcopyright{} 1996 The American Physical Society.

Ejected electrons from the doublet and quartet states of doubly excited ions, produced by 60 keV collisions have been measured with high resolution zero-degree electron spectroscopy. Only the doublet states were observed in collisions with gas. Both doublet and quartet states were observed when was used as the target. Two theoretical methods, perturbation theory or Z-expansion (MZ code) and multi-configurational Hartree - Fock (Cowan code) were used for identification of peaks observed in ejected-electron spectra. Contributions of correlation effects are discussed by comparison with other theoretical energies.

Ejected electrons from the singlet and triplet states of doubly excited O4+ (1s23l3l') and O4+ (1s23l4l') ions, produced by 60 and 120 keV O6+ (1s2) 1S+X collisions (X identical to He, Ne, Ar), have been measured with high resolution zero-degree electron spectroscopy. Only the singlet states were observed when He gas was the target. In contrast, mainly triplet states were observed when Ne gas was used. Both singlet and triplet states contributed to the electron spectra, produced by O6+ (1s2) 1S+Ar collisions. Two theoretical methods, perturbation theory or Z-expansion (MZ code) and multiconfigurational Hartree-Fock (Cowan code) were used for identification of ejected-electron spectra. The contribution of correlation effects is discussed by comparison with other theoretical energies.

Ejected electron spectra from doubly-excited beryllium-like ions produced by collisions of helium-like ions with targets have been measured by using zero-degree Auger electron spectroscopy with a high energy-resolution. The energy of the triplet states of doubly-excited configurations were compared with theoretical ones.

Ejected electrons from the triplet states of doubly excited O4+ ions, produced by 60 keV O6++O2 collisions, have been measured with high resolution zero-degree electron spectroscopy. The triplet states of doubly excited configurations are selectively produced through double electron transfer processes with the O2 molecular target under single collision conditions. Electrons ejected from the 1s22pnl and 1s23lnl' configurations are observed over a wide energy range. Ejected-electron spectra from the O4+(1s23l3l') are compared with theoretical calculations. The calculation of energy levels of 1s23l3l' states has been carried out by the Z-expansion method, where Z is the nuclear charge. Correlation, relativistic and radiative effects are taken into account. Electrons from triplet states are identified by comparison with the calculations and the 'singlet state' spectrum produced by O6++He collisions.

Ejected-electron spectra have been measured for collisions of He-atoms with Na+-ions, whose impact energy ranged from 1.7 to 7.0 keV. The ion impact-energy dependence of the angular-differential cross-section of the ejected electrons has been investigated for an aligned autoionizing state Na**(2p5 3s22P), which has been created by charge transfer from the He-atoms. The alignment of the autoionizing state Na**(2p5 3s22P) is discussed in relation to the scattering angles of the Na+-ions. A complete longitudinal alignment has been observed with respect to the quasimolecular axis.

Partial ionization cross sections for 4 d -electrons in xenon by electron impact have been measured by means of a combination of the electron-energy-loss spectroscopy and the Auger electron spectroscopy in the impact energy region from 70 eV to 4 keV. The cross sections increase with the impact energy rapidly from the threshold and display a sharp maximum, whose value is (17.0 ± 3.5) × 10 -18 cm 2 , around 120 eV impact energy, revealing an existence of a resonance. The cross sections arise again from a minimum at about 200 eV and exhibit a broad maximum of (14.5 ± 3.0) × 10 -18 cm 2 around 500 eV. Absolute scale of the cross section is determined using the generalized oscillator strengths for the 4 d -ionization, which are measured by the electron-energy-loss spectroscopy. Relative cross sections are measured as a function of the impact energy using an Auger line assigned to the N 5 O 2,3 O 2,3 ( 1 S 0 ) line. Experimental results are compared with a previous experimental result given by a different proc...

Ejected electron spectra from the doubly-excited helium-like ions produced by the double electron capture collisions of bare ions B5+ and C6+ with He have been measured using zero-degree Auger electron spectroscopy with a high energy resolution. Electrons from the configuration of (2lnl') have been observed for n>or=2 in B5+-He collisions and n>or=3 in C6+-He collisions. Experimental energy values of ejected electrons from the (2l2l') and (2l3l') states of B3+ ions and the (2l3l') states of C4+ ions are determined by comparing the observed spectra with the theoretical calculations. Spectral features have also been observed at different collision energies. The population mechanisms to those states are briefly discussed.

Ejected electrons from helium-like doubly-excited carbon and boron ions, produced by C6+ and B5+ with He collisions, were measured by the zero-degree electron spectroscopy technique. Electrons from configurations 21nl’ were observed in a wide energy range.

Differential cross sections (DCS) for the 1 {sup 1}{ital S}{minus}2 {sup 3}{ital S} excitation in helium have been measured with a high angular resolution of about 1{degree} as a function of the scattering angle {theta} from 12{degree} to 0{degree} for the incident energies of 200 and 500 eV. For the incident energy of 500 eV, the DCS increases drastically as the angle decreases in the angular range smaller than 4{degree} and reaches a value 0.075 {ital a}{sub 0}{sup 2}/sr at {theta}=0{degree}, the increase being nearly 3 orders of magnitude. The DCS at zero scattering angle for impact energies from 200 to 800 eV have been measured. The DCS's are found to be about 1 order of magnitude greater than those of published measurements by Skerbele, Harshbarger, and Lassettre (J. Chem. Phys. 58, 4285 (1973)) and Klump and Lassettre (J. Chem. Phys. 62, 1838 (1975)).

Ejected electrons from doubly-excited helium-like carbon ions, produced by 67 keV C6++He collisions, were measured with high resolution zero-degree electron spectroscopy. Electrons from the configuration of 2lnl' (n>or=3) were observed in a wide energy range. Ejected electron energies from the 2l3l' configuration were determined and compared with theoretical calculations.

The technique of crossed electron-ion beams has been employed to measure the absolute cross sections for single ionization of Ne 2+ , Ar 2+ , Kr 2+ and Xe 2+ ions at electron energies ranging from below threshold to 1000 eV. Detailed descriptions of the experimental apparatus and procedures to determine the absolute cross sections are presented, and are discussed check points for reliability and consistency as well as possible contributions of metastable contents in the ion beam. The total systematic error in the cross sections is estimated to be within ±9%. A distinct discrepancy is observed for Ne 2+ between the measured cross section curve and results of semiempirical calculation using the Lotz formula. The cross sections for Ar 2+ , Kr 2+ and Xe 2+ reveal significant contributions from excitation-autoionization processes in addition to direct ionization, especially in the near threshold energy regions.

Polarization of the 7 3S 6 3PJ radiation from the Hg atom was observed under electron impact with an energy a little above the 6 1S 7 3S threshold excitation energy. The observing direction was perpendicular to both the incident electron beam and the atomic beam. All of the triplet radiation (J = 0, 1 and 2) was slightly polarized. The observed degree of fractional polarization was -3.07, 1.98 and -0.33%, corresponding to J = 0, 1 and 2 spectra in the final 3PJ states of the Hg atom, respectively. These values could be explained by assuming unequal populations in the sublevels Ms = 0 and ±1 of the 7 3S states, deviating from an equal mean value of (1/3) for each sublevel. The deviation value of the fractional population for the sublevel Ms = 0 was 0.348±0.004.

Electron spectra ejected from doubly excited states of Be-like ions produced by two electron capture processes in O6+ + Ca, C4+ + Mg and C4+ + Ca collisions have been measured by means of high resolution zerodegree electron spectroscopy. For the O6+ + Ca collision, spectra from the 1s24lnl' and 1s25lnl' states are observed in addition to those from the 1s23lnl' states in which n equals six or larger. For the C4+ + Mg and Ca collisions, spectra from the 1s23lnl' and 1s24lnl' states are observed. Population distributions of the states are explained as a whole using the concept of the reaction window based on the extended classical over-barrier model by Niehaus.

Differential cross sections and generalized oscillator strengths have been measured for two optically allowed transitions 2${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}2${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{1/2,3/2}$)3s and the optically forbidden transition 2${\mathit{p}}^{6}$${(}^{1}$${\mathit{S}}_{0}$)\ensuremath{\rightarrow}2${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{1/2}$)3p in Ne. These measurements are carried out for electron kinetic energies 300, 400, and 500 eV at small scattering angles (\ensuremath{\theta}=2.4\ifmmode^\circ\else\textdegree\fi{}--33.7\ifmmode^\circ\else\textdegree\fi{}) by means of electron-energy-loss spectroscopy. Optical oscillator strengths have been determined by extrapolating the generalized oscillator strengths to zero momentum transfer, as (0.137\ifmmode\pm\else\textpm\fi{}0.018) and (0.0106\ifmmode\pm\else\textpm\fi{}0.0014), for the 2${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{1/2}$)3s and 2${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)3s states, respectively. Integrated cross sections have been calculated by integrating the differential cross sections for each impact energy. The errrors are estimated to be less than 13%.

Ejected electron spectra from the double‐excited helium‐like and beryllium‐like ions produced by the double electron capture collisions of bare or helium‐like ions with targets have been measured by using zero‐degree Auger electron spectroscopy with a high energy resolution. Singlet and triplet states of doubly excited configurations were made by the double electron capture processes, selectively.

Electron energy spectra arising from collisions between He-like ions (O6+ and N5+) and rare gas atoms (He, Ne and Ar) were measured using zero-degree Auger electron spectroscopy with high energy resolution. The electrons were ejected from doubly excited Be-like ions produced by double electron capture from the targets. Triplet states in the doubly excited systems were predominantly produced in O6+-Ne and N5+-Ar collisions.

Ejected electrons from doubly-excited helium atoms, produced by double electron capture collisions of He2+ with Mg, Ca and Ba atoms at low energies, have been measured using zero-degree electron spectroscopy with high energy resolution. Electrons from the configurations (2lnl') (n ≥ 2) were observed. Electron spectra from the terms of higher angular momenta are dominant in contrast to the case of ion or electron-impact excitation of neutral He.

Ejected electrons from helium-like doubly-excited carbon and boron ions, produced by C6+ and B5+ with He collisions, were measured by the zero-degree electron spectroscopy technique. Electrons from configurations 21nl were observed in a wide energy range.

Post-collision interaction is investigated on the spectra of Ar L 3 M 23 M 23 Auger electrons which are created by electron impact of energies from 257 eV up to 2000 eV. The spectral shape has been analyzed by taking into account the finiteness of the velocities of both the receding and Auger electrons. Disappearance of the post-collision interaction is found at the highest electron-impact energies.

Measurements have been carried out on the spectra of ejected electrons from atomic autoionising states which are excited by slow Rb++Ar and Cs++Kr collisions. The spectral profiles have been analysed assuming the presence of both the Doppler effect and the Barker-Berry effect. The lifetime of Rb 4p55s2 2P3/2 state is found to be 8.5*10-14 s. A lifetime of 8.0*10-14 s is obtained for the Cs 5p56s2 2P3/2 state.

Ejected-electron spectra from doubly excited helium are measured at several ejection angles for lithium ions of impact energies 2, 3, 4 and 5 keV. Violent variations are observed in the ejected-electron profiles with the changes of ejection angle and impact energy. An especially drastic change with angle is observed at 2 keV.

Spectra of electrons ejected from doubly excited states of helium have been extensively measured at several observation angles for impact of lithium ions at energies lower than 5 keV. "Molecular-autoionization" spectra have been found at forward observation angles, and analyzed in terms of the Gerber-Niehaus theory with modification. The spectral shapes of atomic-autoionization peaks have been discussed in relation to both the Barker-Berry effect and the Doppler effect. Excitation cross sections of autoionizing states have been determined by a new method that uses simultaneous impact of ions and electrons.

The first observation of resonant structures is reported in the double ionization cross section in Ba + as a function of electron-impact energy, which are attributable to the 4d-ionization and the 5s-ionization followed by the autoionization. A brief description of the experimental method and procedures is presented. A discussion is also presented to provide a solid foundation to the identificaticn of the indirect processes concerned. Experimental results are compared with tentative results of the calculation using the distorted-wave Born exchange approximation by Younger.

The f 3 Pi g state of molecular fluorine, which is assumed to be the upper level of a VUV F2 laser at 157 nm, has been directly observed for the first time by high-resolution electron energy loss spectroscopy at low impact energies (less than about 30 eV) and large scattering angles. The new transitions consist of several vibrational components at 11.62, 11.75, 11.86 and 11.99 eV, and show every characteristic feature of spin-forbidden transitions.

Cross sections for single and double ionization of K + and Na + by electron impact have been measured as a function of electron energy from their respective threshold to approximately 1500 eV with the use of the electron-ion crossed-beam technique. The results for single ionization of Na + and K + are in good agreement with the previous crossed-beam data within the experimental uncertainties. Contributions from an autoionization and an L-shell direct ionization followed by autoionization (Auger effect) have been found in the results of single and double ionization cross sections for K + .

Absorption cross sections and photoionization efficiencies of I 2 have been measured in the 600 to 1000A region by the double and single ion-chamber methods, using a He continuum light source, with a resolution of about 2A. The absolute photon intensity was determined by calibrating the chamber with Ar and Xe gases. In this wavelength region, the absorption spectrum of I 2 consisted only of a smooth ionization continuum, and no band structure was found. The absorption cross section decreases monotonically with respect to photon energy from the value of 100 Mb at 1000A to the value of 25 Mb at 600A. There is, however, some undulation superposed on the downward sloping curve, with a kind of shoulder at about 740A. This observation may be explained by the interference effect in the photoionization of molecules which was first suggested by Cohen and Fano. Ionization efficiencies of less than 1.0 were observed in the range of about 820A and above, and at shorter wavelengths they were observed to be equal to or...