Excitation Of Inner-shell Electrons Research Articles

Electron impact ionization of multicharged ions

Computations have been made of the electron-impact ionization cross sections of multicharged ions of C, O, N, Ne, and Ar in the binary-encounter approximation. For ions of the four lighter species, the dominant ionization mechanism is that of direct electron ejection to the continuum. For Ar, excitation of inner-shell electrons to unoccupied bound levels with subsequent autoionization can also make a significant contribution to the total ionization process for some ions. The calculated binary-encounter values are in reasonable agreement with recent experimental data and with the quantum-mechanical calculations of Trefftz for O/sup +4/ and O/sup +5/. (AIP)

Z−1-expansion calculation of two-particle correlations in atoms

A calculation of the expectation value of the mass-polarization operator $〈{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{2}〉$ for the two-electron atom is made using the ${Z}^{\ensuremath{-}1}$ perturbation expansion in order to determine the usefulness of this approach in calculating two-particle correlations in atoms. Evaluation of the first-order contribution to $〈{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{2}〉$ yields a value in good agreement both with an earlier value determined by another method and with the value which may be deduced from calculations using very accurate wave functions. An interesting feature of the calculation is the finding that the summations are dominated by contributions from matrix elements which involve continuum states, with more than 85% of the total coming from these contributions. The second-order contribution is then obtained by demonstrating that both first- and second-order contributions are included in the first-order formula if accurate uncorrelated wave functions for the ground state are used in the matrix elements, rather than the bare hydrogenic orbitals. After observing that most of the greater accuracy of such wave functions arises from inclusion of electronic screening, the first-order calculation is repeated using simple screened hydrogenic orbitals in the matrix elements. The values of $〈{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}_{2}〉$ obtained by means of this simple calculation for various $Z$ values agree quite well with those calculated by Hart and Herzberg using accurate 20-term wave functions. The conclusion which is drawn from this calculation is that this method appears to be relatively simple and quite promising for calculating certain types of correlation effects, such as those resulting from double excitation or ionization of valence or inner-shell electrons. As examples of this, qualitative estimates are made of the behavior of the double photoionization cross sections of the remainder of the He isoelectronic sequence ($Z\ensuremath{\ge}3$) and of other closed-shell atoms.

Influence of electronic correlation effects on the photoionization of sodium and potassium

Various electronic correlation effects associated with the photoionization of alkalis are examined in detail by the use of many-body perturbation theory. With the inclusion of all important correlation effects, in particular, the effect of virtual excitation of inner shell electrons, the author removed most of the existing discrepancies between experimental observations and theoretical calculation.

Effects of inner shell excitation on the stopping power of solids for heavy ions

The range of 100 keV heavy ions in aluminium has previously been found to decrease sharply as a function of the ion's atomic number near Z 1 = 59. This is attributed to the excitation of inner-shell electrons in collisions where energy-level matching occurs.

Laser evaporation and elemental analysis

The preparation of thin uniform targets from multielemental samples by pulsed-laser evaporation is described. The targets are useful in trace elemental analyses employing x-ray or charged-particle excitation of inner-shell electrons. The results of brass and tool-steel analyses are presented as a demonstration of the potential of this application of laser evaporation.

Vacuum Ultraviolet Absorption of Dense Plasmas with Resonance Series of Be, B, C, N, Mg, Al and Si

AbstractAbsorption spectra of light elements were observed in the vacuum ultraviolet with an original technique described in an earlier paper (Mehlman-Balloffet and Esteva, 1969). The method utilizes a two-vacuum spark mounting: one of the sparks is emitting the continuous background, the other one generates the absorbing plasma. Several light element have been successsively introduced in the spark anode. For all of them new autoionizing levels have been observed in Rydberg series of resonances exhibiting the asymmetric ‘Beutler-Fano’ profile.In the beryllium and magnesium spectra three new series corresponding to two-electron excitation process have been identified while for boron, carbon, nitrogen, aluminium and silicon the resonances observed correspond to single subshell electron excitation such as: 2s22p2P0 → 2s2p(3P0)np2De for the case of boron.All these series lie in the photoionization continuum of the absorbing atomic species and usually between the first and second ionization limit. This means that they were observed with a normal incidence grating spectrograph in the spectral range 500–1500 Å. In the extreme ultraviolet some other transitions involving inner-shell electron excitation were observed. In the beryllium spectra a series lying between 100 and 110 Å was identified while, the magnesium spectra exhibited only isolated resonances in the 220-265 Å range together with an inner-shell 2p electron photoioniation continuum.A complete description of experimental results with numerical data is being submitted for publication (Esteva and Mehlman-Balloffet, 1972).

Vacuum ultraviolet absorption of dense plasmas with resonance series of Be, B, C, N, Mg, Al and Si

Absorption spectra of light elements were observed in the vacuum ultra-violet with an original technique described in an earlier paper (Mehlman-Balloffet and Esteva, 1969). The method utilizes a two-vacuum spark mounting: one of the sparks is emitting the continuous background, the other one generates the absorbing plasma. Several light element have been successsively introduced in the spark anode. For all of them new autoionizing levels have been observed in Rydberg series of resonances exhibiting the asymmetric ‘Beutler-Fano’ profile. In the beryllium and magnesium spectra three new series corresponding to two-electron excitation process have been identified while for boron, carbon, nitrogen, aluminium and silicon the resonances observed correspond to single subshell electron excitation such as: 2s 22p 2 P 0 → 2s2p(3 P 0)np 2 D e for the case of boron. All these series lie in the photoionization continuum of the absorbing atomic species and usually between the first and second ionization limit. This means that they were observed with a normal incidence grating spectrograph in the spectral range 500–1500 A. In the extreme ultraviolet some other transitions involving inner-shell electron excitation were observed. In the beryllium spectra a series lying between 100 and 110 A was identified while, the magnesium spectra exhibited only isolated resonances in the 220–265 A range together with an inner-shell 2p electron photoioniation continuum. A complete description of experimental results with numerical data is being submitted for publication (Esteva and Mehlman-Balloffet, 1972).

Multiple Ionization of Ar and Mg by Electron Impact

Ionization efficiency curves (IE curves) of Ar and Mg are measured up to 100 eV by crossed beam method. A mass spectrometer is used for separation of multiply charged ions. Abundance ratios of multiply charged ions to singly charged ion at 500 eV are obtained up to five fold and three fold charge for Ar and Mg respectively. The summations of the IE curves of multiply charged ions agree well with the absolute total ionization curves obtained by other workers. The IE curve of Ar + has two maxima at 45 eV and 90 eV. Remarkable structures are found at 255 eV for Ar 3+ and Ar 4+ and they are attributed to an Auger process or an electron shake-off caused by the ionization of inner shell electrons. A break at 55 eV for Mg 2+ is probably attributed to autoionization arising from the excitation of inner shell electron which occurs below 55 eV. The curves for Ar 2+ , Mg + and Mg 3+ seem to have no structures.

Single and Double Ionization of Na, K and Mg by Electron Impact

The ionization efficiency curves for Na + , Na ++ , K + , K ++ , Mg + and Mg ++ are studied with essentially monoenergetic electrons. It is proved that Na + , K + and Mg + follow the linear law up to 1.5 eV, 0.8 eV and 2 eV above the thresholds, respectively, and that Na ++ and K ++ follow the square law up to about 20 eV and 15 eV above the thresholds, respectively. These results agree with the theoretical prediction that n-fold multiple ionization would be proportional to a n-th power of excess electron energy. Two remarkable humps are found in the I. E. curve for Mg + , which are attributed to autoionization processes, These processes occur at 2.3±0.1 eV and 5.0±0.2 eV above the ionizotion potential, the first one may correspond to the excited states of Mg atom, 1 F° and 3 D°, but any excited states to be correlated to the second one is not known. Contrary to expectation, the I. E. curve for Mg ++ is not a square curve of excess energy but has a complex shape. In order to explain the shape, possibility of autoionization due to excitation of inner shell electron is suggested.