High-energy Born collision strengths for optically forbidden transitions

Abstract

Collision strengths for optically forbidden transitions in positive ions excited by electron impact tend to finite limits as the energy of the colliding electron becomes infinitely great. This statement applies to theoretical data obtained by means of approximations which ignore relativistic effects. The high-energy limiting values are given by the Born approximation, which Bethe showed can be reduced to a closed expression requiring integration over momentum transfer and the radial distance of the atomic orbital. In the appendix we describe an accurate numerical procedure for evaluating this double integral and also show how to perform the Racah algebra which arises when mixed configurations are used to describe the target. We make applications to several isoelectronic sequences taking configuration interaction into account.

Atomic data for astrophysics: Fe x soft X-ray lines

“…6× 10 11 103.319 100.39 1-30 3s 2 3p 5 Burgess & Tully (1992) scaled domain. The high-energy limits were calculated with autostructure for both optically-allowed (see Burgess et al 1997) and non-dipole allowed transitions (see Chidichimo et al 2003). All the transitions from the ground configuration were visually inspected.…”

Atomic data for astrophysics: Fe xi soft X-ray lines

“…These limits are particularly important for two reasons. First, they allow a consistency check on the collision strengths in the scaled Burgess & Tully (1992) domain (see also Burgess et al 1997). Second, they are used in the interpolation of the collision strengths at high energies when calculating the Maxwellian averages.…”

“…The high-energy limits were calculated with autostructure for both optically-allowed (see Burgess et al 1997) and nondipole allowed transitions (see Chidichimo et al 2003). The temperature-dependent effective collisions strength Υ(i − j) were calculated by assuming a Maxwellian electron energy distribution.…”

Atomic data from the IRON project

“…At higher energies we used the method of scaling and extrapolating to the appropriate high-energy limits as described in Burgess & Tully (1992). The high-energy limits were calculated with AUTOSTRUCTURE for both optically-allowed (see Burgess et al 1997) and forbidden transitions (see Chidichimo et al 2003).…”