SYMBOLS FOR FINE AND HYPERFINE-STRUCTURE PARAMETERS

The symbols for fine and hyperfine structure parameters are standardiz ed in order to eliminate confusion and misunderstanding caused by vari ous uses of expressions for these parameters. Only those parameters fo r which the symbols are quite well established and widely accepted are considered. Because the parameters appear with the associated operato rs in the Hamiltonian, the symbols are listed with the operators. Alth ough much of the discussion is appropriate for molecules in the gas ph ase 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: li near and nonlinear molecules. The parameters listed include the spin-o rbit 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-d ipole coupling, the nuclear electric quadrupole coupling, and the nucl ear spin-rotation coupling parameters and also their centrifugal corre ction terms, wherever appropriate.