Periodic Table

At any time you may choose the molecule that you are interested in from the list below the table. Using the periodic table helps to narrow this list down.

Back to the table

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 approximately 1% of the lines are radio waves and 1% are infrared.

Isotopes

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

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 in the ASCII version
P or Pi	Π
D or Di	Δ
W	Ω
S	Σ
X1-S	X1Σ
A1-S	A1Σ

Frequency

The observed transition frequency is given in megahertz.

Unc.

The estimated uncertainty is also given in megahertz. In most cases the uncertainties and the transition frequency measurements are reported directly from the original reference. Note: 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. If only an X appears, then it is to indicate that the uncertainty is unknown.

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 angular momentum quantum number, excluding nuclear spins.
N	Resultant angular momentum quantum number, excluding electron and nuclear spins, in the case where electron spin is present.
F1	Resultant angular momentum quantum number including nuclear spin for one nucleus.
F	Resultant total angular momentum quantum number.
X	Quantum number employed when F1 is not a good quantum number. This value simply numbers the levels from lowest to highest energy for the same F quantum number.
∋	Vibrational quantum number.

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 this link will take you to the original data reference. 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.