This is the first part of a series of articles reporting critically evaluated thermochemical properties of selected free radicals. The present article contains datasheets for 11 radicals: CH, ${\mathrm{CH}}_2(\mathrm{triplet}\mathrm{),}$ ${\mathrm{CH}}_2(\mathrm{singlet}\mathrm{),}$ ${\mathrm{CH}}_3,$ ${\mathrm{CH}}_2\mathrm{OH},$ ${\mathrm{CH}}_3\mathrm{O},$ ${\mathrm{CH}}_3\mathrm{CO},$ ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O},$ ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2,$ OH, and ${\mathrm{NH}}_2.$ The thermochemical properties discussed are the enthalpy of formation, as well as the heat capacity, integrated heat capacity, and entropy of the radicals. One distinguishing feature of the present evaluation is the systematic utilization of available kinetic, spectroscopic and ion thermochemical data as well as high-level theoretical results.

The determination of equilibrium structures of molecules by spectroscopic methods or by quantum mechanical calculations is reviewed. The following structures are described in detail: experimental equilibrium structures, empirical structures, semi-experimental structures and ab initio structures. The approximations made by the different methods are discussed and their accuracies are compared.