Spectral Data Options

Frequency Range Search

You can search for a particular frequency range by using this field. If you use only the left text field, then your search will be for any frequencies greater than or equal to the frequency you enter. If you use only the right text field, then your search will be for any frequencies less than or equal to the frequency you enter. You can make your search in either megahertz or gigahertz. Most of the data is for the microwave region, however some (less than 1%) of the lines are infrared.

Molecules

You can limit your search to any of the the molecules listed. The number of spectral lines given for each molecule is listed in parenthesis.

$, *, and _

Pairs of these symbols indicate the begining and ending of a bond.

ASCII output

You can choose to have the output returned in ASCII format rather than an HTML table. The ASCII table is better for copying and pasting, but the HTML table looks better when printed.

Column Descriptions

Molecular Species

This is the molecular species to which the data pertains.

Special Characters
PI	Indicates the symbol Π in the ASCII version.
$, *, and _	Pairs of these symbols indicate the begining and ending of a bond.

Frequency

The observed transition frequency is given in megahertz.

Unc.

The estimated uncertainty is also given in megahertz. Note: Since the maximum number of significant figures beyond the decmial 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 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. A hash mark (#) located in front of the uncertainty denotes that the frequency is the hyperfine free center of the frequency.

Quantum Numbers

The quantum numbers are given in the sequence: rotational and hyperfine for the upper state (primed quantum numbers), then rotational and hyperfine for the lower state (double primed quantum numbers).

J	Resultant total angular momentum quantum number, excluding nuclear spins.
N	Rotational angular momentum quantum number, excluding electron and nuclear spins, in the case where electron spin is present.
K-, K+	Projection of J (or N) on the symmetry axis in the limiting prolate or oblate symmetric top.
F1	Resultant angular momentum quantum number including nuclear spin for one nucleus.
F	Resultant total angular momentum quantum number.
A, E	Torsional symmetry substates representing irreducible representations of the symmetry group of the rotation-internal rotation Hamiltonian.
ν1,ν2,ν3	Vibrational modes (ν) and quantum numbers (v).
U or L	Upper or lower energy level or transition frequency.
ℓ	Quantum number for vibrational angular momentum.
I or (Ii)	Angular momentum quantum number of nuclear spin for one (or ith) nucleus.

Parity

Parity is a property of a state (electronic, vibrational, etc.) or the wavefunction describing the state as either even (+) or odd (-) character.

Ref.

Following the link contained in the "Ref." column will take you to the original data reference. Reference data is suppressed if the reference is the same as the last reference shown. Following the link for the "Ref." column heading will take you to a page where you can search for references.