Abstract:
The B-spline R-matrix method was used to study electron-impact excitation of carbon from threshold to 60 eV. A multi-configuration Hartree-Fock method with non-orthogonal orbitals generated a very accurate target description. The close-coupling expansion included the bound and autoionizing states of neutral carbon derived from the (1s2)(2s2)(2p2),(1s2)(2s2)(2p)(3s),(1s2)(2s2)(2p3p),(1s2)(2s2)(2p3p),(1s2)(2s2)(2p4s),(1s2)(2s2p3), and (1s3)(2p4) configurations, plus pseudo-states to fully account for the polarizability of the ground state. Our predictions for the cross sections show significant discrepancies with those from previous calculations carried out with the standard R-matrix approach in a similar scattering model. These discrepancies are mostly due to the different target descriptions. The cross sections for excitation from the ground state (2p2)3p and the metastable (2p2)1d and (2p2)1s states also exhibit prominent resonance structures in the low-energy region. Classifications for these resonances will be presented.
