Single Ionization Of Helium Atom Research Articles

Using a post-version continuum distorted wave formalism for calculation of the fully differential cross section of helium atom single ionization by proton impact

In the present work, the fully differential cross section of single ionization of helium atom is calculated by fast proton impact. The calculations are done as a four-body formalism and by using a post-version continuum distorted wave theory with considering symmetric wave functions in the both initial and final channels. The ionization is considered from the ground and $$2^{1}S$$ excited states of helium atom. In order to investigate the role of the static electronic correlations, the calculations are performed by single-parameter Hylleraas and two-parameter Silverman as the ground state of helium atom wave functions. The results of the present theory are compared with the experiment in 1MeV proton impact energy and various values of the ejected electron energy and momentum transfer in the scattering and azimuthal planes. The results show that the present theory is able to predict the binary and recoil peaks as well as the experiment for ejected electron energies and momentum transfers are discussed in this manuscript.

Applying a four-body continuum-distorted-wave formalism in calculating the fully differential cross section for single ionization of helium in collision with high-energy protons

The present study aimed to calculate the fully differential cross section for single ionization of helium atom by fast protons impact. These calculations are performed as four-body formalism by applying the continuum-distorted-wave method, considering the wave functions symmetrically in the initial and final channels. The dependence of this theory on the ground-state wave functions of the helium in the initial channel is investigated through performing calculations for the three wave functions Hylleraas, Silverman and Silverman-Platas-Matse, respectively. In addition, the effect of inter-nuclear interaction in determining the dynamics of collision for all three wave functions is investigated. Comparing the results of the present theory with the experimental results in the 1 MeV impact energies of protons, the 6.5 eV electron ejection energies and 0.75 a.u transferred momentum in the scattering plane and azimuthal plane indicates that this theory can accurately predict binary and recoil peaks and determine the dynamics of collision at the energies discussed in the paper.

Fully differential cross-sections in single ionization of helium by 2 MeV/amu C6+ impact: The role of correlated wave functions

We study the effect of final-state dynamic correlation in single ionization of helium atom by 2 MeV/amu C6+ impact analyzing the fully differential cross-sections (FDCS). The transition matrix is introduced using a correlated continuum wave (CCW) and that for the initial state by an undistorted Born-approximation. The final state is modeled by the CCW function so that both the correlation and the interaction between the projectile and the residual target ion (PT interaction) are treated. The analytical expression of the transition matrix has been obtained through a series representation of the CCW function. Illustrative computations are performed in the scattering plane. A comparison of fully differential results using the present model with other theories and experimental data reveals that the dynamic correlation is responsible for the enhancement of the FDCS structure. The PT interaction is also checked in our model. We observe a satisfactory, although not perfect, agreement of the CCW calculations with experimental findings. Large discrepancies between the experimental data and theoretical predictions are found, which can at least be partly attributed to the inclusion of dynamic correlation effects.

Towards XUV pump-probe experiments in the femtosecond to sub-femtosecond regime: New measurement of the helium two-photon ionization cross-section

Non-linear photoionization of molecules in the 10–50eV range is a prerequisite for pump-probe measurements with sub-femtosecond resolution, but hitherto has been limited to femtosecond resolution, low repetition rate and high photon flux laser systems. We demonstrate two-photon single ionization of helium atoms using 100pJ, 1.34fs pulses (main peak FWHM=680 as) at 1kHz repetition rate with a central photon energy of 19.6eV. We obtained an exponent of 2.27±0.21 for the intensity dependence of the signal and a two-photon ionization cross-section of 5.0±0.5×10−50cm4s. Our work opens the possibility of attosecond pump-probe measurements of ultrafast molecular processes.

Triple differential cross section for the near threshold single ionization of helium atoms for equal energy sharing

Low energy electron impact single ionization triple differential cross section (TDCS) results are reported for the helium atoms in the threshold regime at 1eV, 3eV and 5eV excess energy. TDCSs are calculated in the doubly symmetric kinematics for the coplanar to perpendicular emission of electrons. Present attempt to calculate TDCS in the second Born approximation and treating target polarization and post collision interaction is helpful to analyze the available measurements. The second order processes, target polarization and post collision interaction (PCI) have been found to be significant in describing the trends of TDCS and helpful to produce reasonably good agreement with measurements.

Single ionization of helium atoms by energetic fully stripped carbon ions

A four-body distorted wave approximation is presented for theoretical investigations of the single ionization of ground-state helium atoms by fully stripped carbon ions at impact energies of 2 MeV/amu and 100 MeV/amu. The nine-dimensional integrals for the partial quantum-mechanical transition amplitudes of the specified reaction are reduced to some analytical expressions or one-dimensional integrals over real variables. Fully differential cross sections (FDCSs) are calculated and compared with their experimental values as well as the results obtained from other theories. Despite the simplicity and quickness of the proposed quadrature, the comparison shows that the obtained results are in reasonable agreement with the experiment and are compatible with those of other complicated theories.

Electron correlation in fast ion-impact single ionization of helium atoms

A four-body distorted-wave approximation is applied for theoretical analysis of the fully differential cross sections (FDCS) for proton-impact single ionization of helium atoms in their ground states. The nine-dimensional integrals for the partial amplitudes are analytically reduced to closed-form expressions or some one-dimensional integrals which can be easily calculated numerically. Calculations are performed in the scattering and perpendicular planes. The influence of the target static electron correlations on the process is investigated using a number of different bound-state wave functions for the ground state of the helium targets. An illustrative computation is performed for 75-keV proton-helium collisions and the obtained results are compared with experimental data and other theoretical predictions. Although for small momentum transfers, the comparison shows a reasonable agreement with experiments in the scattering and perpendicular planes, some significant discrepancies are still present at large momentum transfers in these planes. However, our results are compatible and for some cases, better than those of the other sophisticated calculations.

A four-body approach to electron-impact single ionization of helium atoms

A four-body approach based on the three-Coulomb distorted wave (3CDW) model is applied to study of the electron-impact single ionization of helium atoms. Triply differential cross sections (TDCS) are calculated for different values of the incident and ejection energies and various amounts of the scattering angles. The ejection angular distribution of the TDCS in general exhibits two peaks, binary and recoil peaks. The obtained results are compared with the available experimental data as well as other theoretical predictions. The comparison shows a good agreement between the present calculations and the measurements. Also, the obtained results are compatible with the other theories.

Projectile angular distribution in He single ionization by proton impact as a function of the ejected-electron energy

In this paper we study the single ionization of helium atoms by the impact of protons at intermediate energies. We present a continuum-distorted-wave--eikonal-initial-state calculation of the cross section doubly differential in the projectile scattering angle and the ionized electron energy. The internuclear interaction is incorporated by means of an eikonal phase approximation. This calculation includes a full account of the final-state interactions among the three collision partners, showing a much better agreement with the recent experimental data of Schulz et al. than other first-order theories. We also discuss the appearance of different structures associated with the electron capture to the continuum process and the binary-encounter projectile-electron collision.

CDW-EIS calculations for recoil ion emission in proton—helium collisions

Single ionization of helium atoms in collision with high energy protons is treated theoretically in the continuum distorted-wave eikonal initial-state (CDW-EIS) approximation. The total $\langle $E$\_{\text{R}}\rangle $ and transverse $\langle $E$\_{\text{R}\perp}\rangle $ average He$^{+}$ recoil-ion-energies are calculated as functions of the laboratory proton scattering angle $\Theta \leq $ 2 mrad. Measurements (Dorner et al. 1989, Phys. Rev. Lett. 63, 147-150) of these average energies made for helium gas in equilibrium at 30 K are reasonably well reproduced to within a factor of two, by the CDW-EIS approximation. The CDW-EIS recoil-ion energy distributions are convoluted over a Maxwellian-Boltzmann distribution, to allow for the 30 K thermal motion of the target helium atoms in the experiment.

Energy and angular distributions of electrons emitted and ions recoiled in proton-impact ionization of helium atoms

Single ionization of helium atoms in collisions with high-energy protons is theoretically treated in the eikonal distorted-wave approximation. The momentum and angular distributions of the ejected electrons and the recoil ions are calculated as functions of the proton scattering angle.