Electron-impact excitation of Co2+

Electron-impact excitation cross sections and Maxwellian-averaged rate coefficients are calculated from the ground 3d(7) F-4 to the first 3d(7) P-4 and the second 3d(7) (2)G excited terms in Co2+ in close coupling with 8 and 27 terms; much larger transition arrays were first explored in a distorted-wave approximation. Both transitions are important elements of the emission spectrum of type Ia supernovae. We find that the two excitations are dominated by autoionizing resonances attached to higher-lying excited terms in the 3d(7) 3d(6)4s, 3d(6)4p, and 3d(6)4d configurations. Those LS terms that are strongly excited from the ground 3d7 4F, as found by distorted-wave calculations, are included in a large R-matrix calculation using asymptotics based on multichannel quantum defect theory. [S1050-2947(98)06510-X].