The NIST Physics Program produces the most comprehensive set of reliable physical reference data available anywhere. The NIST collection of atomic energy levels, transition probabilities, and collision data is widely used by groups for characterizing and modeling all types of gaseous systems, including plasmas, planetary atmospheres, and astrophysical media, and for health physics applications. Databases and publications make these data easy to find and easy to use. The physics online databases have grown into an extensive listing. The NIST Chemistry WebBook now contains electronic and vibrational spectra for over 5000 compounds. The WebBook also contains constants of diatomic molecules.
NIST has also produced several important compilations of molecular data.
NIST Thermophysical Properties of Hydrocarbon Mixtures
NIST XCOM: Photon Cross Sections Database