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A numerical method based on Zabaydullin and Dubau's work [O. Zabaydullin and J. Dubau, J. Phys. B: At. Mol. Opt. Phys. 45, 115002 (2012)] has been developed to calculate the Cauchy principal value integral in scattering matrices and obtain photorecombination (PR) cross sections of low-lying resonances according to Davies and Seaton's theory [J. Phys. B 2, 757 (1969)], in which radiation damping is included. The Dirac R-matrix method is employed to secure the dipole matrix. Using this method, PR cross sections of C4+ for the KLL resonance are acquired, and compared with available experimental measurements and other close-coupling theoretical results. It is shown that our damped cross sections reproduce the experimental data and are in agreement with other theoretical results. Meanwhile, radiation damping can reduce the PR cross section for the 1s2p² ²P resonance (corresponding to two levels [(1s2p1/2)12p3/2]1/2 and [1s(2p²3/2)2]3/2 by three orders of magnitude. The unresolved and underestimated resonances 1s2p² 4P, 1s2s2p 4P, and 1s2p² ²P in the undamped Breit-Pauli R-matrix calculations [H. L. Zhang et al., J. Phys. B: At. Mol. Opt. Phys. 32, 1459 (1999)] are corrected. Besides, dielectronic recombination cross sections of C4+ for the KLL resonance are also presented for comparison using the relativistic configuration-interaction (RCI) method implemented in flexible atomic code (fac), which show radiation damping has pronounced influences on 1s2p² ²P due to much larger radiative rates compared with autoionization rates. Furthermore, radiative and autoionization rates for the intermediate states [(1s2p1/2)12p3/2]1/2 and [1s(2p²3/2)2]3/2 of the He-like ions with 6≤Z≤83 are calculated using fac, scaling laws of which are checked. Autoionization rates comply with the Z0eff scaling law for Z≥32, which is caused by relativistic effects. [ABSTRACT FROM AUTHOR]

A multicenter distorted-wave (MCDW) method for fast-electron-impact single ionization of a molecular system in the coplanar-asymmetric kinematics is developed. Plane waves are used to describe the fast incoming and outgoing electrons and the multicenter nature of the molecule is considered by describing the slow ejected electron with the multicenter distorted wave, which is solved from the anisotropic multicenter potential between the ejected electron and the ionic molecule. The MCDW method improves the conventional molecular distorted-wave methods, whose distorted wave is solved from the spherically averaged isotropic potential. The application to the water molecule shows reasonable agreement with the available experimental data. [ABSTRACT FROM AUTHOR]