Electron impact excitation of the iron peak element Fe II

Abstract

Effective collision strengths for electron-impact excitation of Fe II are presented for all sextet-to-quartet transitions among the 38 LS states formed from the basis configurations 3d64s, 3d7 and 3d64p. A total of 112 individual transitions are considered at electron temperatures in the range 30–100 000 K, encompassing values of importance for applications in astrophysics as well as laboratory plasmas. A limited comparison is made with earlier theoretical work and large differences are found to occur at the temperatures considered. In particular, it is found that the inclusion or omission of some (N + 1)-bound configurations in the Hamiltonian matrices describing the collision process can have a huge effect on the resulting effective collision strengths, by up to a factor of four in some cases.

Uncertainty estimates for theoretical atomic and molecular data

“…Instead, one should concentrate on an observable that is more stable regarding small changes in the individual predictions, but which is still meaningful in modeling applications. Such an observable is the effective collision strength, where an integral over the incident energies [197,198] for the 5 D e partial-wave collision strength of the electron-induced transition (3d 6 4s) 6 D − (3d 7 ) 4 F in Fe + . [197] are compared with those of Nussbaumer and Storey (NS80) [199], Pradhan and Berrington (PB93) [200], and Ramsbottom et al [198].…”

“…Such an observable is the effective collision strength, where an integral over the incident energies [197,198] for the 5 D e partial-wave collision strength of the electron-induced transition (3d 6 4s) 6 D − (3d 7 ) 4 F in Fe + . [197] are compared with those of Nussbaumer and Storey (NS80) [199], Pradhan and Berrington (PB93) [200], and Ramsbottom et al [198]. For highly charged ions, as electron correlation effects are less important, perturbative methods such as PWBA, DWBA produce comparable results to nonperturbative methods as long as the structure description is reliable.…”

An analysis of the optical spectra of the post-asymptotic giant branch stars LSIV -12 111 and HD 341617

“…Unfortunately the limited spectral coverage does not provide an independent electron temperature diagnostic for HD 341617, and hence we have simply adopted the value found by CDMK93 for LSIV −12 111, i.e. T e = 7800 K. We note that Parthasarthy et al (2000) have derived a nebular temperature of T e = 10 000 K for HD 341617 from [Fe ] line ratios, but this must be treated with caution given the uncertainties in atomic data for this ion (Ramsbottom et al 2002). However the [O ] and [Fe ] line ratios employed here are relatively insensitive to temperature, and hence the density estimates discussed below are effectively independent of the adopted electron temperature.…”

Electron-impact excitation of Fe II: Effective collision strengths for optically allowed fine-structure transitions

“…Subsequent works by Baluja et al [6], Berrington et al [7], Keenan et al [8], Pradhan and Berrington [9], Zhang and Pradhan [10], Bautista and Pradhan [11] and Ramsbottom et al [12][13][14] have increased the sophistication of the theoretical models describing the Fe II target. The most extensive and accurate set of collisional data currently available for the Fe II ion were computed by Ramsbottom et al [15].…”