It is suggested that the term, a, describing the difference between gas phase and solid state XPS data is related to the molar polarizability P by the general expression a = b p−1/3 + c From previously obtained values of the parameters b and c (b= 8.30 eV cm mol−1/3and c= 4.15 eV) we can derive the binding energy of gaseous carbon atoms, Eb= 296.4 eV. The close agreement with the experimentally found Eb= 296.2 eV is regarded as a validification of the above-mentioned formula and also of the concept of atomic charge.