NIST: Diatomic Molecules - General Description of Tables

1. General Description of the Tables

Two types of tables are presented for each molecular species. The first table contains the derived molecular constants for each isotopic species which has been studied. and the second table (accessed through an online form) contains the observed microwave spectrum for all isotopic forms of the molecule.The molecular spectral data tables of section 6 are available with a table of the derived internuclear distances for all molecules included in the review.

Literature references are labeled with a number from one of the two systems employed here. In the first system. reference numbers range from 1 to approximately 2000 and are identical to the bibliography compiled by Favero [2]. The second system, which utilizes 5 digit numerals, has been formulated such that the first two digits refer to the year of publication of the reference work, while the remaining three digits correspond to a chronological ordering within the year as required for referencing purposes here. It is anticipated that this second technique, which has more degrees of freedom, will be utilized entirely in the forthcoming parts of this series on polyatomic molecules.

a. Molecular Constant Tables

Since a uniform format could not readily be constructed for these tables, they were composed in variable format depending on the type of data available. In general, the rotational constants are listed first, followed by hyperfine structure data, electric dipole moments, rotational g-factors and finally, the molecular reduced mass which was utilized in many isotopic substitution calculations.

b. Spectral Line Tables

The spectral tables contain all of the data intrinsic to an assigned molecular transition. The first column of these tables contain the isotopic molecular species to which the data pertain. Each isotopic species is followed by the assigned quantum numbers in the sequence: rotational, hyperfine, and vibrational. The next columns contain the observed transition frequency, its estimated uncertainty, parity when relevant, and finally the reference to the original source of the data. In all cases the quantum numbers referring to a particular transition frequency are listed with the upper energy state (primed quantum numbers) first, followed by the lower energy state designation (double primed quantum numbers). Since the vibrational state remains unchanged for all transitions, a single quantum number, italic v

, is sufficient. In most cases the uncertainties and the transition frequency measurements are reported directly from the original reference. Since the number of significant figures beyond the decimal point was fixed in this compilation, in a few cases it was necessary to round off the measured data. This situation occurs primarily in the reproduction of molecular beam measurements. Thus, when an uncertainty of ±0.01 MHz is quoted in the spectral line tables, the uncertainty is often less than ±10 kHz, while a quoted uncertainty of ±0.00 MHz generally means the uncertainty is less than ±1 kHz. When uncertainties in the transition frequencies 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. A hash mark (#) located in front of the uncertainty denotes that the frequency is the hyperfine free center of the frequency.

A concerted effort was made to locate all of the essential references through mid 1973. 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. In several instances this procedure was not rigorously followed when the same transitions were reported in many publications over a period of years with improved accuracy in each case. In these cases only the more recent and most accurate citations are indicated.