  We analyze the experimental hadron yield ratios for central nucleus-nucleus
collisions in terms of thermal model calculations over a broad energy range,
$\sqrt{s_{NN}}$=2.7-200 GeV. The fits of the experimental data with the model
calculations provide the thermal parameters, temperature and baryo-chemical
potential at chemical freeze-out. We compare our results with the values
obtained in other studies and also investigate more technical aspects such as a
potential bias in the fits when fitting particle ratios or yields. Using
parametrizations of the temperature and baryonic chemical potential as a
function of energy, we compare the model calculations with data for a large
variety of hadron yield ratios. We provide quantitative predictions for
experiments at LHC energy, as well as for the low RHIC energy of 62.4 GeV. The
relation of the determined parameters with the QCD phase boundary is discussed.
