The threshold photoelectron spectrum (TPES) of iron pentacarbonyl Fe(CO)(5), is obtained over an energy range 5-35 eV using a synchrotron radiation source. Ab initio calculations at a level of theory more refined than Koopmans' theorem yield ionization potentials in better agreement with experiment and allow the assignment of the origin of most of the observed bands in the TPES on the basis of a decomposition in (quasi) local contributions. From the measured appearance threshold of FeC+ the bond energy D-0(Fe+-C) = 84.2 +/- 4.1 kcal/mol is obtained, and the enthalpy Delta H-f(Fe+-C) = 366.0 +/- 6.0 kcal/mol is derived.