Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV

Abstract

We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths, and subsequently the excitation rates, the Dirac Atomic Rmatrix Code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are provided for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 10 8 K. Comparisons are made with similar data obtained using the Flexible Atomic Code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, particularly for some forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.2

Electron impact excitation of Be-like ions: a comparison of darc and icft results

“…We believe the discrepancies have arisen mainly due to some compromises made by Fernández-Menchero et al ( 2014) in calculating Ω and subsequently Υ, as noted in section 2. Similar large discrepancies between the two independent R-matrix approaches have also been noted in the past -see for example, Aggarwal & Keenan (2014b) for Fe XIV, Aggarwal & Keenan (2013b) and references therein for He-like and Aggarwal & Keenan (2012a) for Li-like ions. Therefore, it appears that the implementation of the ICFT approach, although computationally highly efficient (hence allowing data for many ions to be produced over relatively short periods), may not be completely robust.…”

Division B Commission 14 Working Group: Collision Processes

“…Several large-scale efforts to calculate excitation data for iso-electronic sequences have been undertaken. For He-like ions data is now available covering most ions from Mg 10+ to Kr 34+ (Aggarwal & Keenan 2012b, Aggarwal & Keenan 2012d, Aggarwal & Keenan 2012e, Aggarwal & Keenan 2012c, Aggarwal & Keenan 2013b, Aggarwal & Keenan 2013c.…”