Ionization–excitation magnetic sublevel cross sections for He+(2p)2P0 states following fast electron and proton impact (original) (raw)
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Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
Experimental magnetic sublevel scattering-angle-integrated cross sections following ionization-excitation of He(1s 2 ) 1 S to He + (2p) 2 P o in e − + He and H + m +He (m = 1-3) collision systems have been determined using a combination of total cross sections and polarization fraction measurements in the extreme ultraviolet range. The derived magnetic sublevel cross sections, σ 0 and σ 1 , for M L = 0 ± 1 have been studied over a wide range of velocities (2-8.5 au) for electron impact on helium. These results are compared with previous experimental proton cross sections (2-6 au) as well as new measured data for hydrogen molecular impact (1.4-4.0 au) for equi-velocity. In addition, our electron and proton measurements are compared with earlier theoretical predictions, our recent second-Born calculations fully including off-shell energy terms, and present predictions from a hybrid first-order and second-order distorted-wave plus R-matrix (close-coupling) model (DWB1 + RMPS and DWB2 + RMPS). Finally, we have extended our polarization measurements for H + + He collisions and found excellent agreement between theory and experiment at nearly all impact energies. However, the present second-Born and DWB1 + RMPS results deviate slightly from the experimental electron data while the DWB2 + RMPS calculations tend toward the experimental data of Forand et al (1985
Simultaneous ionization-excitation of helium to He^{+}(2p) magnetic sublevels by proton impact
Physical Review A, 2001
Experimental magnetic substate cross section ratios 0 / 1 and scattering angle-integrated cross sections following ionization-excitation of helium to He ϩ (2p) 2 P o in H ϩ ϩHe collisions have been determined, using polarization measurements of emitted radiation in the extreme ultraviolet region in combination with total cross sections, over a wide range of proton velocities ͑2-6 a.u.͒. These results are compared with second Born calculations fully including off-energy terms for the He ϩ (2p) 2 P o sublevels. We have found good agreement between theory and our He ϩ Lyman-␣ measurements.
2003
Experimental scattering-angle-integrated (total) cross-sections r r, (scattering) angle-integrated magnetic sublevel cross-sections r r ML , and degree of linear polarization data have been measured in the extreme ultraviolet (EUV) wavelength region following decay of HeI ð1snpÞ 1 P 0 ðn ¼ 2-5Þ states induced by electron and proton impact on a neutral helium target. These measurements are compared with a first Born approach as well as more sophisticated theoretical calculations. Specifically, theoretical values for electron impact include convergent close-coupling (CCC) and R-matrix with pseudo states (RMPS) methods in addition to first Born (Born 1) approximation while proton induced excitation cross-sections are compared with atomic-orbital close-coupling (AOCC) and first Born predictions.
Atomic Data and Nuclear Data Tables, 2003
Experimental scattering-angle-integrated (total) cross-sections r r, (scattering) angle-integrated magnetic sublevel cross-sections r r ML , and degree of linear polarization data have been measured in the extreme ultraviolet (EUV) wavelength region following decay of HeI ð1snpÞ 1 P 0 ðn ¼ 2-5Þ states induced by electron and proton impact on a neutral helium target. These measurements are compared with a first Born approach as well as more sophisticated theoretical calculations. Specifically, theoretical values for electron impact include convergent close-coupling (CCC) and R-matrix with pseudo states (RMPS) methods in addition to first Born (Born 1) approximation while proton induced excitation cross-sections are compared with atomic-orbital close-coupling (AOCC) and first Born predictions.
Physical Review Letters, 1993
We present the total ionization cross section and spin asymmetry at projectile energies ranging from threshold to 500 eV for electron-impact excitation of atomic hydrogen. They are calculated using the convergent close-coupling formalism of Bray and Stelbovics [Phys. Rev. A 46, 6995 (1992)]. Both observables are found to be in complete quantitative agreement with measurements over almost the entire energy range. This is the only electron-atom scattering theory that is able to achieve this result to date.
Electron-impact-excitation cross sections of hydrogenlike ions
Physical Review A, 1997
Convergent close-coupling ͑CCC͒ and Coulomb-Born with exchange and normalization ͑CBE͒ methods are used to study electron-impact excitation of hydrogenlike ions. The nl→nЈlЈ cross sections demonstrate ͑i͒ good agreement between the CCC and CBE results, ͑ii͒ a scaling over ion nuclear charge z, ͑iii͒ a domination of the dipole (lЈϭlϮ1) contributions in total n→nЈ cross sections, and ͑iv͒ significant effect of electron exchange in the energy range xϽ3 ͑here x is the ratio of the incident electron kinetic energy to the transition energy E n,n Ј ). For ions with zϾ5 the n→nЈ cross sections obtained in the CCC and CBE approximations agree with each other to better than 10% for any x. An accuracy of the cross sections scaling over z 4 depends on z: for zϭ6 -18 the scaling is accurate to better than 10% ͑quantitative analysis is done for nЈϽ7), for ions with zϽ6 the cross sections deviate from the z 4 scaling more significantly ͑at x about unity͒. The n→nЈ cross sections are presented by a formula which fits our CCC and CBE results with an accuracy to better than 10% ͑for transitions with nϽnЈϽ7 in ions with zϾ5). The new Gaunt factor G(x) suggested for the widely used Van Regemorter formula ͓Astrophys. J. 136, 906 ͑1962͔͒ makes this formula accurate to better than 50% in the xϾ3 range and to better than 20% in the xϾ100 range. It is shown that the semiempirical formula by Vainshtein, Sobelman, and Yukov ͓Electron-Impact Excitation Cross Sections of Atoms and Ions ͑Nauka, Moscow, 1973͔͒ provides an accuracy to better than 50% for any incident electron energy. For xϽ2 this formula is accurate to better than 30%. These accuracy assessments are based on a comparison with our CCC and CBE results.
Vector (e, e ) correlations in ionization excitation of He by electron impact
Journal of Physics B: Atomic, Molecular and Optical Physics, 2002
The general description of simultaneous electron-impact ionization-excitation processes is reformulated in terms of an irreducible tensor representation. Using a numerical model, in which the interaction between a 'fast' ionizing projectile and the target is described by first-or second-order plane-wave and distortedwave models, combined with a convergent close-coupling-type description of the initial bound state and the interaction between a 'slow' ejected electron and the residual ion, new benchmark calculations for the (e, e γ ) process have been performed. The predictions are compared with recent experimental data on ionization-excitation of helium. The similarity to results for excitation processes and the potential extension of propensity rules is discussed.
Physical Review A, 2001
Experimental cross sections in the extreme ultraviolet ͑EUV͒ wavelength range for the excitation of helium following electron and H ϩ , H 2 ϩ , and H 3 ϩ ion impact are presented for He I (1snp) 1 P o states with n ϭ2 -5. These measurements extend over large velocity ranges 3.8-8.5 a.u. for electrons, 1.4-7.5 a.u. for protons, and 1.4-4.0 a.u. for H 2 ϩ and H 3 ϩ ions, respectively, and represent the most complete data set obtained so far in the EUV. Furthermore, the methods of convergent close coupling and R matrix with pseudostates have been used here to predict excitation cross sections for the He I (1snp) 1 P o states following electron impact and the atomic-orbital close-coupling expansion for proton impact. In particular, our theoretical results are presented and compared with our EUV experimental cross sections for equal projectile velocities together with previous experimental results, including cross sections derived from scaling procedures. The electron cross sections are found to deviate from the proton data at intermediate and lower energies (vϽ3.8 a.u.).
Physical Review A, 2003
We report experimental and theoretical electron spectra within the very low-electron-energy range below 30 eV. Doubly differential cross sections for ionization of different noble gases ͑He, Ne, Ar, Kr, Xe͒ by impact of 100-keV and 225-keV protons are reported. A pronounced structure in the low-energy region of emittedelectron spectra is observed with different intensities for the different targets. We compare our experimental findings with two theoretical models: the first-order Born approximation and the ''continuum-distorted-waveeikonal-initial-state'' model using different optimized central potentials to calculate the bound and continuum states of the target. We attribute our experimental observation to a signature of the predicted low-energy binary peak.
Physical Review A, 2019
We present a theoretical investigation of the single ionization of He in collisions with H + projectile ions at 75-keV impact energy. Using the frameworks of the independent-electron model and the impact parameter picture, fully differential cross sections (FDCS) are evaluated in the continuum distorted-wave with eikonal initial-state approximation (CDW-EIS). Comparisons are made to the recent measurements of Schulz et al. [Phys. Rev. A 73, 062704 (2006)] and Arthanayaka et al. [J. Phys. B: At. Mol. Opt. Phys. 49, 13LT02 (2016)]. Strong influence of the internuclear interaction and effects of target core polarization due to the presence of the projectile ion are observed. Comparing the present results to experimental data and other theoretical predictions, it has been found that the CDW-EIS method qualitatively reproduces structures in the FDCS. Projectile coherence effects are investigated by representing the projectile beam as a Gaussian wave packet. Evidence of interference effects due to projectile-electron and projectile-target core interactions are discussed and the need for further theoretical investigations is proposed.