Since a uniform format could not be readily constructed for these tables, they were composed in variable format depending on the type and amount of information available. In general, the rotational constants are listed first, followed by the centrifugal distortion parameters, hyperfine structure data, electric dipole moments and rotational g-factors. In cases where extensive data are available, several individual tables are used to present the molecular constants. A more detailed description of the molecular constants and their symbols is given in section 2.
The spectral tables contain all of the data intrinsic to an assigned molecular transition. The first column of these tables contains the isotopic molecular species to which the data pertain. The next columns contain the assigned quantum numbers for the transition in the sequence: rotational and the hyperfine for the upper state. rotational and hyperfine for the lower state, and vibrational state designation. Since the vibrational state remains unchanged for nearly all transitions, a single set of quantum numbers, (υ1,υ2ℓ,υ3), is sufficient. The next columns contain the observed transition frequency, its estimated uncertainty, and finally the reference to the original source of the data. Since the maximum number of significant figures beyond the decimal point was fixed at three for the transition frequency and two for uncertainties, in a few cases it was necessary to round off the measured data. This situation occurs primarily in the reproduction of molecular beam measurements. When the uncertainty in the measurement is less than 0.01 MHz, the exponential notation is employed. Thus, an uncertainty of 0.005 MHz appears as 5E-3, which represents 5 x 10-3 MHz. When uncertainties were not given in the original source, an uncertainty was assigned on the basis of the internal consistency of all the data available for the molecule in question. Predicted transition frequencies have been given for several isotopic forms of HCN, H2O, H2S, and OCS. In order to distinguish these from measured transitions, an asterisk (*) was placed in front of the estimated uncertainty, which is twice the standard deviation from the fit.
An effort was made to locate all of the essential references through mid-1976. In situations where multiple measurements have been reported, the sources not directly cited here are included as additional references at the end of the molecular constant tables. These additional references also include publications which are indirectly related to the frequency measurements and which contain intensity measurements.