text: Dissociative photoionization processes can be generalized as:
  If the enthalpies of formation of two of the three species are known, the third can be calculated with the help of the dissociative photoionization energy, E, using Hess's law. This approach was used, for instance, to determine the enthalpy of formation of the methyl ion, , which in turn was used to obtain the enthalpy of formation of iodomethane,  as 15.23 kJ mol, with an uncertainty of only 0.3 kJ mol.
  If different sample molecules produce shared fragment ions, a complete thermochemical chain can be constructed, as was shown for some methyl trihalides, where the uncertainty in e.g. the , (Halon-1021) heat of formation was reduced from 20 to 2 kJ mol. Furthermore, dissociative photoionization energies can be combined with calculated isodesmic reaction energies to build thermochemical networks. Such an approach was used to revise primary alkylamine enthalpies of formation.