#### Abstract

Observations of the relative line strengths of Beryllium like ions in a high temperature plasma can be used to derive the electron temperature and density of the emitting region through diagnostic line ratios [1,2]. However, to calculate such ratios reliably, accurate atomic data must be employed, especially for the electron impact excitation rates of the relevant transitions [3]. In this paper we compare the theoretical S XI11 and Ar XV emission line ratios R1 = I (2s2p 'P 2s' IS) / I (2s2p 3P 1 2s2 IS), and R2 =I ( 2 ~ 2 ~ 'P 2s2 IS) / I (2p2 3Pz 2s2p 3P2) with observational data for several solar flares, obtained using the S082A instrument on board Skylab. Good agreement is found between theory and observation for R1 for both ions, which provides support for the electron impact excitation rates adopted in the calculations. However, in the case of R2, all the observed values for S XI11 and Ar XV are much smaller than the theoretical estimates, which is probably due to blending in the 2p2 3P2 2s2p 3P2) lines.