Rotational spectral lines for 121 diatomic molecules, 55 triatomic molecules, and 91 hydrocarbon molecules have been tabulated. The isotopic molecular species, assigned quantum numbers, observed frequency, estimated measurement uncertainty, and reference are given for each transition reported. The spectral lines for many molecules and normal isotopic species have been refit to produce a comprehensive and consistent analysis of all the data extracted from various literature sources. The derived molecular properties, such as rotational and centrifugal distortion constants, hyperfine structure constants, electric dipole moments, rotational g-factors and internuclear distances (for diatomic molecules) are listed with one standard deviation uncertainties for all species.

In addition to the interface for each molecule, this online version of these three databases contains a multiple-molecule, frequency-searchable interface for the diatomic, triatomic, and hydrocarbon molecules and an updated, searchable reference database.