Electron temperature diagnostics for the quiet Sun using SiIV lines

We compare SUMER observations of six Si IV emission lines detected at the q uiet Sun disk centre with recent theoretical line ratio calculations. Good agreement is found between theory and observation for ratios involving the 1394, 1403 and 818 Angstrom line intensities. This agreement supports the t heoretical prediction that the temperature where Si IV has its maximum ioni sation fraction in ionisation equilibrium is T-max similar or equal to 10(4 .8) K, as well as showing that Lyman continuum absorption does not signific antly effect line intensities for transitions with wavelengths below 912 An gstrom. We find that the 815, 1122 and 1128 Angstrom lines are blended by a pproximately 30, 55 and 45%, respectively, in the SUMER transitions.