Electron impact excitation cross section for the 1s–2s transition in H-like Fe. The cross sections have been convolved with a 25 eV FWHM Gaussian distribution. The solid line shows the DARC results with radiation damping included, the dashed line show the ICFT results with radiation damping included. The dot-dashed line shows the semi-relativistic CADW results with radiation damping included. The solid squares show the direct excitation calculated using a fully-relativistic distorted-wave method. The solid circles show the DARC calculation of Aggarwal et al. (2008).