Electron Ejection Angle Research Articles

0 degrees binary encounter electron production in 30-MeV Oq++H2, He, O2, Ne, and Ar collisions.

Double-differential cross sections (DDCS's) for the production of binary encounter electrons (BEE's) were measured for collisions of 30-MeV ${\mathrm{O}}^{\mathit{q}+}$ projectiles with ${\mathrm{H}}_{2}$, He, ${\mathrm{O}}_{2}$, Ne, and Ar targets with q=4--8 and an electron ejection angle of \ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{} with respect to the beam direction. Particular interest focused on (a) the evaluation of the contributions of the different electron subshells of the multielectron targets, ${\mathrm{O}}_{2}$, Ne, and Ar; (b) the study of the well-known enhancement of the BEE DDCS's with decreasing projectile charge-state q; here this dependence was tested for higher collision energies and new targets; (c) the study of the dependence of the BEE peak energy on the particular target and projectile charge state. Results were analyzed in terms of the impulse approximation, in which target electrons in the projectile frame undergo 180\ifmmode^\circ\else\textdegree\fi{} elastic scattering in the field of the projectile ion. The electron scattering calculations were performed in a partial-wave treatment using the Hartree-Fock model. Good agreement with the data was found for the ${\mathrm{H}}_{2}$ and He targets, while for the multielectron targets ${\mathrm{O}}_{2}$, Ne, and Ar only electrons whose velocity was lower than the projectile velocity needed to be included for good agreement. All measured BEE DDCS's were found to increase with decreasing projectile charge state, in agreement with other recent BEE results. The BEE peak energies were found to be independent of the projectile charge state for all targets utilized. \textcopyright{} 1996 The American Physical Society.

A study of resonant behaviour in the photoelectron band of sulphur hexafluoride

Angle-resolved photoelectron spectra encompassing the and the states of sulphur hexafluoride have been recorded in the 20 - 22 eV photon energy range using synchrotron radiation. The envelope of the photoelectron band displays a complicated structure which varies significantly both as a function of excitation energy and as a function of electron ejection angle. The data for the state have been analysed by dividing the band into eight regions, specified by their binding energies. The results show that, as the photon energy is varied, the branching ratio for each region exhibits an enhancement at an electron kinetic energy of about 2.5 eV. The photoelectron angular distributions also vary significantly across the band. Various interpretations for this resonant behaviour are discussed.

Zero-degree binary encounter electron production in 30 MeV bare O8+ in collisions with H2, He, Ne, Ar, Kr and Xe

Double differential cross-sections for the production of binary encounter electrons were measured for collisions of 30 MeV bare O8+ projectiles with H2, He, Ne, Ar, Kr and Xe targets at an electron ejection angle of θ = 0° with respect to the beam direction. Results were analyzed in terms of the impulse approximation (IA), in which target electrons in the projectile frame undergo 180° Rutherford scattering in the field of the bare projectile ion. Excellent agreement with the data was found for the H2 and He targets, while for the multi-electron targets good agreement was established only when target electrons whose velocities were lower than the projectile velocity were included in the calculation.

Vibrational distribution of N2+A ²Πu from 100‐eV electron impact on N2

Measurements of the electron excitation of the Meinel band system of N2+ produced by electron impact on N2 have been hampered by the long lifetime of the N2+ A 2Πu upper state, the spectroscopically inconvenient near‐infrared region where the bands are located, as well as overlap by the N2 first positive system. In the present work, an experiment in which the scattered projectile electron and the low‐energy secondary electron are detected in coincidence was used to allow the vibrational distribution of the A 2Πu state produced by 100‐eV electron impact on N2 to be determined directly in excitation without the need for optical measurements. The coincidence energy loss spectrum was measured for a typical secondary electron energy of 5 eV over a range of secondary electron ejection angles. The results of a band contour analysis show that the population of the ν′=0‐5 vibrational levels is consistent with that predicted by the Frank‐Condon factors for ionization of N2 to the N2+ A 2Πu state.

Influence of nuclear track potentials in insulators on the emission of target Auger electrons.

The angle, energy, and fluence dependence of electron emission following the interaction of normally incident 100-MeV ${\mathrm{Ne}}^{9+}$ ions with thin polypropylene foils and 170-MeV ${\mathrm{Ne}}^{7+}$ projectiles with Mylar foils has been investigated experimentally. Spectra were taken for electron ejection angles of 0\ifmmode^\circ\else\textdegree\fi{}, 45\ifmmode^\circ\else\textdegree\fi{}, and 120\ifmmode^\circ\else\textdegree\fi{} at fluences in the range of 2\ifmmode\times\else\texttimes\fi{}${10}^{13}$ to 4\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ions/${\mathrm{cm}}^{2}$. A fluence-dependent carbon KLL Auger energy shift of up to 68 eV was observed. Model calculations for the nuclear track potential are consistent with the experimental findings.

Evidence for electron correlation in the two-electron continuum during double ionization in 300-keV H++He collisions.

Absolute differential ionization probabilities for small impact parameter H{sup +}+He collision were measured as a function of the electron energy, electron ejection angle, and final recoil-ion charge state. Good agreement was found between an experimental angular distribution of ejected electrons and results of a coupled-channel calculation in the case of single ionization. In the case of double ionization, significant discrepancies to theoretical predictions are found, indicating a breakdown of the independent electron model. Furthermore, evidence is provided that dynamic correlation effects in the two-electron continuum strongly influence the angular distribution of ejected electrons for double ionization.

Charge sign dependence of autoionization resonance profiles produced by protons and antiprotons

Strong sign charge dependence for the autoionization resonance shape in electron emission spectra has been found for ionization of helium by protons and antiprotons. It appears to be more pronounced at small ejection angles and should be observed experimentally. Moreover ionization collisions with antiprotons can be used for spectroscopic measurements of autoionization resonance characteristics at those electron ejection angles.

Population of projectile-ion states during the passage of high energy ne-ions through thin carbon foils

Abstract Absolute doubly differential electron emission yields have been measured for high energy Ne-ions (3.5 to 8.5 MeV/u) penetrating C-foils of thicknesses between 5 and 100 μg/cm2 under normal incidence. Spectra were obtained for electron energies from 10 eV to 6 keV and electron ejection angles ranging from 0° to 180°. Results of a new theoretical model for the transport of electrons in dense matter are compared to the experimental data. From the comparison it was possible to deduce the population of projectile ion states inside the solid.

K- and L-shell electron emission from carbon atoms by antiproton and proton impact.

Electron emission from the {ital K} and {ital L} shells of carbon by 1-MeV antiproton and proton impact is studied. Double differential cross sections as a function of the electron ejection energy and angle are calculated using the continuum-distorted-wave--Eikonal-initial-state model. Contributions to the formation of a recently measured anticusp from electrons of different shells is analyzed for impact of antiprotons. The same effect is studied for the capture-to-continuum peak that appears for proton impact.

Ionisation of helium by antiproton and proton impact

Single-electron ionisation of helium atoms by impact of antiprotons and protons is studied. The continuum-distorted-wave-eikonal-initial-state model is employed. Calculations of double differential cross sections, as a function of the final electron energy and for fixed electron-ejection angles, are given. A dip in the energetic region of electrons moving with low momentum with respect to the projectile is analysed. The importance of describing the dynamics of the electron in the simultaneous fields of the projectile and of the residual target is demonstrated.

Double differential cross sections for electron ejection from helium by fast protons

The authors present measurements of the cross sections for the ejection of electrons from helium atoms by protons, differential in the electron ejection angle and energy. The proton energies range from 20 to 100 keV, while the electron energies range from 5 to 100 eV and the ejection angles from 0 to 100 degrees . The measurements are normalised by comparing the estimates of the total cross section, derived from double integration of the measured distributions, with published absolute values of the ionisation cross section. Although the energy distribution agrees with existing data, there is a substantial divergence in the angular behaviour. As the measurements include the zero-degree region, the electron capture into the continuum (ECC) peak is examined in detail and an estimate of the total cross section for this process is made over a range of proton energies.

Three-photon resonance ionization of H2

Calculations are performed for the ionization of para-H2 by absorption of three 6.6 eV photons. Two photons are absorbed to excite H2 to the E, F 1Σ+g state, and a third photon is absorbed to ionize this state. The two-photon Rabi rate and one-photon ionization rate are linear in the laser intensity (I) and are thus competitive. This competition produces a strong dependence of the three-photon ionization rate on the vibrational-rotational levels of the bound–bound electronic transition and on the electron ejection angle. For example, for I = 1 GW cm−2 the strong (maximum ionization rate 6×108 s−1/molecule) vJ = 00→v′J′ = 30 transition is 70% saturated at 0° and 100% saturated at 90° ejection angle relative to the linear polarization direction of the photon. The weak (maximum ionization rate 2×1 07 s−1/molecule) vJ = 00→v′J′ = 32 transition is 0.3% saturated at 0° and 80% saturated at 90° ejection angle. These calculations suggest use of multiphoton ionization data to study one-photon excited-state angular distributions. The latter occur for an excited state which has a nonstatistical distribution of rotational M′ sublevels belonging to the J′ level of the excited state (in contrast to the photoionization of a ground state having a statistical distribution of M sublevels belonging to J).

Radiative corrections to atomic photoeffect and tip bremsstrahlung. III

The radiative corrections to the photoeffect from the $K$ shell were evaluated recently by McEnnan and Gavrila assuming a hydrogenlike atomic model. The result was expressed in the form of a corrective factor [$1+(\frac{\ensuremath{\alpha}}{\ensuremath{\pi}})\ensuremath{\delta}$] multiplying the basic photoeffect differential cross section. An expression for $\ensuremath{\delta}$, correct to lowest order in $\ensuremath{\alpha}$ and $\ensuremath{\alpha}Z$, was derived in analytic form in terms of a large number of single and double integrals over Feynman parameters, requiring numerical integration. $\ensuremath{\delta}$ depends on the photon energy $\ensuremath{\omega}$, on the electron-ejection angle $\ensuremath{\theta}$, and on the energy threshold $\ensuremath{\Delta}E$ below which we allow the additional (soft) photon, emitted together with the ejected electron to go undetected. The $\ensuremath{\Delta}E$ dependence of $\ensuremath{\delta}$ reflects the inseparable connection between the $K$-shell photoeffect and the Compton effect from the $K$ shell with (soft) photons emitted in the range $\ensuremath{\Delta}E$. It was shown that the same expression for $\ensuremath{\delta}$ with an appropriate redefinition of the variables, also radiatively corrects the bremsstrahlung spectrum at its high-energy tip. In the present work we have carried out the computation of $\ensuremath{\delta}$. It covers the $\ensuremath{\omega}$ energy range from 0.5 keV to 50 MeV at all relevant angles. The relative error was kept below 0.001, except at high energies where it was only 0.01. We find that ($\ensuremath{-}\frac{\ensuremath{\alpha}\ensuremath{\delta}}{\ensuremath{\pi}}$) is always positive and increases with $\ensuremath{\theta}$ and $\ensuremath{\omega}$. At energies of about 500 keV, ($\frac{\ensuremath{\alpha}\ensuremath{\delta}}{\ensuremath{\pi}}$) becomes of the order of 1% and at 5 MeV it has grown to about 5%, when taking $\ensuremath{\Delta}E=0.01$${\mathit{mc}}^{2}$. By integrating over the angles we have derived the quantity $\ensuremath{\Delta}$ which radiatively corrects the total photoelectric cross section, in the form of a factor [$1+(\frac{\ensuremath{\alpha}}{\ensuremath{\pi}})\ensuremath{\Delta}$]. We also infer by exponentiation the correct form of $\ensuremath{\delta}$ and $\ensuremath{\Delta}$ in the limit $\ensuremath{\Delta}E\ensuremath{\rightarrow}0$. Finally, we derive the expression for the cross section describing the energy spectrum of the electrons emitted in the vicinity of the photoelectric peak, which is the basic information coming from coincidence experiments.

Spin polarisation of photoelectrons ejected from unpolarised atoms

The photoelectrons ejected from unpolarised atoms by polarised or unpolarised light are usually spin polarised. The polarisation for the (nl)N subshell, with l>or=1 and 1<or=N<or=4l+2, arises from spin-orbit splitting at the initial and (or) final states. To observe this polarisation it is necessary to select the photoelectrons corresponding to the transition from a particular fine-structure level of the initial state to a particular fine-structure level of the final state. The effect exists at all photon energies. The degree of polarisation depends on the energy and polarisation of the photons, the angle of electron ejection and the atomic characteristics. After integration over the electron ejection angles the degree of polarisation becomes equal to zero when unpolarised or linearly polarised light is absorbed and remains non-zero for absorption of circularly polarised light. The degree of polarisation of the photoelectrons ejected from the 2p6 and 3p6 subshells of Ar and the 4d10 and 5p6 subshells of Xe, calculated in the random-phase approximation with exchange, is presented.

Energy and angular distributions of electrons ejected from water vapor by 0.3–1.5 MeV protons

Absolute cross sections, differential in electron energy and ejection angle, have been measured for ejection of electrons from water vapor by protons with energies from 0.3 to 1.5 MeV. These cross sections are compared with similar measurements for ionization of molecular hydrogen and oxygen and previously published results for hydrocarbon. The criteria for additivity and scalability of electron ejection cross sections are discussed.

Time-of-flight measurements of low-energy electron energy distributions from ion–atom collisions

A time-of-flight technique for the measurement of the energy spectra of electrons ejected in ion–atom collisions is described. Ionization is produced by a pulsed beam of protons which are obtained by chopping the dc proton beam from a Van de Graaff accelerator with a 3.33 MHz high voltage oscillator. Electron energy and angular distributions are derived from time-of-flight spectra recorded for different emission angles. This system is capable of measurements for proton energies from 0.25 to 2.0 MeV, ejected electron energies from 0.3 eV to several hundred eV, and electron ejection angles from 30° to 150°. The advantages and limitations of this technique are illustrated.

On the shape of the (2s2)1S resonance in the spectra of electrons ejected from He atoms during their encounters with fast electrons and protons

Some aspects of the theoretical description of the intensity and shape of resonances observed in the spectra of electrons ejected from atoms by fast electrons and protons are discussed. Numerical calculations have been performed for the (2s2)1S resonance of helium atoms. Dependences of the resonance intensity and shape on the collision kinematics, i.e. incident-particle energy and electron ejection angle, have been obtained. The considerable variations revealed in the character of the resonance asymmetry with varying ejection angle are associated with a strong interference between separate components of the transition amplitude.