Continuum Distorted Wave-eikonal Initial State Calculations Research Articles

Electron emission from CH4 molecule induced by 5.5 MeV/u bare C ions

SynopsisWe present the experimental and theoretical study of electron emission from methane (CH4) in collisions with 5.5 MeV/u bare carbon projectiles. We have measured double differential cross section of electron emission and compared the data with the prior form of the continuum distorted wave – eikonal initial state (CDW-EIS) model calculation. The CDW-EIS calculations are in very good agreement with the data.

Doubly differential distribution of electron emission in ionization of uracil in collisions with 3.5-MeV/u bare C ions

We report the energy and angular distribution of the electron emission from an RNA base molecule uracil in collisions with 3.5-MeV/u bare C ions. The absolute double differential cross sections (DDCS) are measured for emission energy between a few to 600 eV. The angular distributions are compared to those obtained for the O${}_{2}$ molecule in the same experiment. The single differential cross sections (SDCS) are also deduced. The energy and angular distributions of the DDCS and SDCS are compared with the state-of-the-art quantum-mechanical models based on continuum distorted wave-eikonal initial state (CDW-EIS) and correct boundary first Born (CB1) approximations which use a suitable molecular wave function for uracil. The models, however, give substantial deviations from the observed energy and angular distributions of the DDCS as well as SDCS. The CDW-EIS calculations are closer to the data compared to the CB1. In the case of uracil a large difference in the forward-backward emission of electrons was observed in comparison to that in collisions with an oxygen molecule.

Impact ionization of molecular oxygen by 3.5-MeV/u bare carbon ions

We have measured the absolute double-differential cross sections (DDCSs) for electron emission in ionization of O${}_{2}$ molecules under the impact of 3.5-MeV/u C${}^{6+}$ ions. The data were collected between 10 and 600 eV, in an angular range of ${30}^{\ensuremath{\circ}}$ to ${150}^{\ensuremath{\circ}}$. The single-differential cross sections (SDCSs) in emission angle and electron energy are deduced from the electron DDCS spectra. Also, the total cross section has been obtained from the SDCS spectra. The DDCS spectra as well as the SDCS spectra are compared with continuum distorted-wave eikonal initial-state calculations which employ molecular wave functions built as linear combinations of atomic orbitals. The DDCS ratio i.e. $\ensuremath{\sigma}{{}_{\mathrm{O}}}_{2}/2{\ensuremath{\sigma}}_{\mathrm{O}}$, derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show any primary or secondary oscillations arising from Young-type interference, which is apparently in contrast to what has been observed earlier for H${}_{2}$ and in agreement with the model calculation. Similarly, the forward-backward angular asymmetry increases monotonically with the velocity of the emitted electrons. However, the results on the DDCSs, SDCSs, the asymmetry parameter, and the nonexistence of oscillations are in qualitative agreement with the predictions of the model used.

Strong double K-K transfer channel in near symmetric collision of Si+Ar at intermediate velocity range

We present a combined study of single and double K-K electron transfer cross sections along with the single and double K-shell ionization of Ar induced by Si projectiles in the energy range 0.9-4.0 MeV u-1. The charge-state dependence of the normal and hypersatellite x-rays was used to derive the cross sections for the one- and two-electron processes, respectively. The enhancement in the fluorescence yields due to multiple vacancies was measured from the energy shifts and intensity ratios of the characteristic x-ray lines to derive K-shell vacancy production cross sections from x-ray production cross sections. The ratio of double to single K-K transfer cross sections is found to be quite large for this nearly symmetric collision system, whereas the ratio of double to single ionization cross sections is quite small. The measured single K-K transfer cross sections are reproduced very well by the two-centre close-coupling calculations whereas the double K-K transfer data are underestimated by the theory based on the independent-electron approximation (IEA). The K-shell ionization cross sections are found to deviate strongly from the calculations based on the continuum distorted wave eikonal initial state (CDW-EIS) and ECPSSR models. The CDW-EIS calculations along with the IEA model grossly underestimate the double ionization cross sections. It is stressed that in the case of two-electron processes the independent-electron model breaks down and the possible role of correlations between K-electrons is discussed.

Single ionization of He by ions

The final state longitudinal momentum distributions of the ejected electron, recoil ion and the projectile momentum transfer for are calculated within the continuum distorted-wave (CDW) model at an impact energy of . The results are discussed in the context of recent CDW eikonal-initial state calculations (CDW-EIS) and are compared with available experimental data. The calculated electron energy spectrum and total ionization cross sections within the CDW approximation are in good agreement with both the measurement and the theoretical CDW-EIS calculations.

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.

Comment on ionisation of the first excited state of hydrogen by ion impact using the continuum distorted wave eikonal initial state approximation

The continuum distorted wave eikonal initial state (CDWEIS) approximation is used to study the ionisation of hydrogen in it's first excited state by proton and antiproton impact in the energy range 10–1000 keV. The total cross sections presented are found to be in disagreement with similar CDWEIS calculations by Fainstein, Ponce and Rivarola [6]. It is concluded that Fainstein et al. have erroneously included a constant multiplicative factor (of 2) in their calculations.