Cross Sections For Photoionization Of He Research Articles

Modification of the Endohedral Potential after Instant Ionization of an Inner Atom

We investigate here the variation of endohedral A@CN potential due to instant ionization of an inner atom A. Using a reasonable model to describe the fullerenes shell, we managed to calculate this variation that is a consequence of the monopole polarization of CN shell. We demonstrate that the phenomenological potentials that properly simulate the CN shell should belong to a family of potentials with a non-flat bottom, instead of very often used square well potential. As concrete example, we use the Lorentz-bubble model potential. By varying the shape of this potential, we describe the various degrees of the monopole polarization of the CN shell by positive electric charge at the center of the shell. We calculated the photoionization cross sections of He, Ar, and Xe atoms located at the center of C60 shell with and without taking into account accompanying this process monopole polarization of the fullerenes shell. Unexpectedly, we found that the monopole polarization do not affect the photoionization cross sections of these endohedral atoms, thus presenting a very seldom example of potential conspiracy.

Photoionization-Excitation and Double Photoionization of He@C60

The R-matrix with pseudostates (RMPS) and time-dependent close-coupling (TDCC) methods are used to calculate photoionization-excitation and double photoionization cross sections of He and He@C60.

Electron-He+P-wave elastic scattering and photoabsorption in two-electron systems

In a previous paper [A. K. Bhatia, Phys. Rev. A 69, 032714 (2004)], electron-hydrogen $P$-wave scattering phase shifts were calculated using the optical potential approach based on the Feshbach projection operator formalism. This method is now extended to the singlet and triplet electron-${\mathrm{He}}^{+}$ $P$-wave scattering in the elastic region. Phase shifts are calculated using Hylleraas-type correlation functions with up to 220 terms. Results are rigorous lower bounds to the exact phase shifts, and they are compared to phase shifts obtained from the method of polarized orbitals and close-coupling calculations. The continuum functions calculated here are used to calculate photoabsorption cross sections. Photoionization cross sections of He and photodetachment cross sections of ${\mathrm{H}}^{\ensuremath{-}}$ are calculated in the elastic region---i.e., leaving ${\mathrm{He}}^{+}$ and H in their respective ground states---and compared with previous calculations. Radiative attachment rates are also calculated.

Regularities and irregularities in partial photoionization cross sections of He

We have combined B-spline basis sets with R-matrix theory for the description of photoionization in two-electron systems and applied this combination to the study of irregularities in He photoionization when doubly excited resonances up to the $N=9$ threshold of ${\mathrm{He}}^{+}$ are reached. Both total and partial photoionization cross sections have been obtained. Since the magnitude of the resonance effects is very similar for all partial cross sections, we believe that experimental investigations of photoionization cross sections leaving ${\mathrm{He}}^{+}$ in a highly excited state could provide the most information about possible long-range fluctuations in the photoionization cross sections.

Precision measurements of the total photoionization cross-sections of He, Ne, Ar, Kr, and Xe

Absolute photoionization cross-sections for the rare gases have been measured from threshold to 125 eV with an accuracy of ±1 to 3% and are presented in both tabular and graphical form. These data are compared with the optical oscillator strength measurements of Brion and co-workers, who used the Dipole (e, e) collision technique.

Photoionization Cross Sections of He and H2

Photoionization Cross Sections of He and H₂

Photoionization Cross Sections of He and H2

We combine accurate measurements at low energies and theoretical calculations at high energies to construct sets of photoionization cross sections of He and H2 that should be reliable at all energies. We control the accuracy of the recommended cross section data by ensuring that they satisfy a range of oscillator strength sum rules. We provide accurate analytic formulae for the photoionization cross sections that have the proper asymptotic form. At high frequencies the cross sections for H2 are 2.8 times those for H.

Polarization effect on He doubly excited states below theN=2threshold ofHe+

Based on the R-matrix method, photoionization cross sections of He below the N = 2 threshold of He+ are calculated, and a definite assignment of the doubly excited resonance states is determined by the eigenchannel treatment. Our results are in good agreement with the experimental data and other theoretical works. The polarization effects on the doubly excited states are studied in detail. We elucidate the effects of the dynamic polarization within the reaction zone (i.e., R-matrix box) and the long-range static polarization potentials outside the reaction zone, which influence the resonance energies and the profiles of He resonance states. [S1050-2947(98)00802-6].

Redetermination of absolute partial photoionization cross sections of He and Ne atoms between 20 and 300 eV photon energy

Using photoelectron spectroscopy, we have measured some relative partial photoionization cross sections in He and Ne atoms. By compiling these results, along with previously published data obtained from photoabsorption, photoion and photoelectron spectroscopies, we have determined accurate absolute partial photoionization cross sections, up to 300 eV photon energy. The absolute scale was obtained by normalization to the photoabsorption cross sections. The best recommended values, determined by this self-consistent experimental procedure, are compared with the results of various theoretical determinations of the photoionization cross sections.

Precision measurements of the absolute photoionization cross sections of He

Precision photoionization cross sections for He have been measured from threshold to 120 eV with an accuracy ranging from 1 to 2%. In addition, a critical review of the published data has been made and recommended photoionization cross sections from the ionization threshold to 8 keV are presented with an estimated uncertainty of +or-10% above 500 eV. The effect of coherent (Rayleigh) and incoherent (Compton) scattering is discussed.

Extensive L2 calculation of partial photoionization cross sections of He in the 4lnl' resonance region.

We present a fully-[ital L][sup 2]-integrable calculation of the partial photoionization cross sections of He between the [ital N]=3 and 4 thresholds. The energy positions, total and partial autoionization widths, and Fano and Starace parameters for the 4[ital lnl][prime] doubly excited states lying in this region are also provided. We have found that only one series of resonances with large autoionization widths is observed in the total-cross-section spectrum. On the other hand, several resonance series are exhibited in the partial [ital N]=3 cross sections. Our results also show that the 2[ital p] and 3[ital p] cross sections dominate the [ital N]=2 and 3 ones, respectively. Good agreement with the existing experimental data is found.

L2 calculation of multichannel photoionization parameters in the neighborhood of the 3s3p 1P degrees resonance of He.

We have calculated a complete set of Fano-Starace parameters for partial photoionization cross sections of He in the vicinity of the 3s2p $^{1}$P\ifmmode^\circ\else\textdegree\fi{} resonance, using a recently proposed multichannel ${\mathit{L}}^{2}$ method for continuum wave functions [F. Martriaan, A. Riera, and I. S\'anchez, J. Chem. Phys. 94, 4295 (1991)]. Our results are in good agreement with recent photoabsorption measurements [D. W. Lindle, T. A. Ferrett, P. A. Heimann, and D. A. Shirley, Phys. Rev. A 36, 2112 (1987)] and show the importance of correctly including interaction between the different open channels to interpret the experimental data.