Results from a variety of spectroscopic measurements are necessary for computations in statistical thermodynamics. In particular, calculations of atomic and molecular properties usually require knowledge of electronic energy levels and their associated electronic degeneracies. This appendix provides the appropriate data in tabular form for selected atoms and molecules. The atomic tables include electron configurations, term symbols, and energies (cm−1) for the ground state and five additional upper energy levels. For most degenerate energy levels, mean energies are determined from relevant closely-lying values and reported with one less significant digit. In a similar fashion, the molecular tables provide term symbols and electronic energies (cm−1) for the ground state and three additional upper energy levels. The tabulated molecular energies (Te) represent energy gaps between the minima corresponding to internuclear potentials for the ground electronic and each upper electronic state. The atomic data have been taken from compilations made available electronically by the National Institute of Standards and Technology (NIST) (http://physics.nist.gov/PhysRefData), while the molecular data have been extracted from Huber and Herzberg (1979).