SYMBOLS FOR FINE AND HYPERFINE-STRUCTURE PARAMETERS

The symbols for fine and hyperfine structure parameters are standardized in order to eliminate confusion and misunderstanding caused by various uses of expressions for these parameters. Only those parameters for which the symbols are quite well established and widely accepted are considered. Because the parameters appear with the associated operators in the Hamiltonian, the symbols are listed with the operators. Although much of the discussion is appropriate for molecules in the gas phase only, reference is also made to the symbols used in electron spin or electron paramagnetic resonance spectroscopy in the condensed phase, where possible. Two types of molecules are considered separately: linear and nonlinear molecules. The parameters listed include the spin-orbit interaction, the spin-rotation coupling, the spin-spin coupling, the LAMBDA-type doubling, the electron orbital/nuclear spin coupling, the Fermi contact interaction, the electron spin/nuclear spin dipole-dipole coupling, the nuclear electric quadrupole coupling, and the nuclear spin-rotation coupling parameters and also their centrifugal correction terms, wherever appropriate.