Abstract
By means of arguments based on a thermodynamic cycle, general formulae are derived which express standard field ion appearance energies in terms of atomic parameters and molecular term values, and in terms of thermodynamic parameters. These formulae may be applied to field ionization, field evaporation, or to the field desorption of well-behaved molecules, and apply to a very wide range of desorption mechanisms. Previous theories of energy deficits are reviewed in the light of the general result. The extent of agreement between theory and experiment is assessed, and the need for continued theoretical development is noted. Formulae are provided for converting the variety of energy-deficit parameters encountered in the literature into appearance energies; and the various terminologies are correlated.