Instructions / Help
The periodic table can be used to determine the database's holdings.
Those elements with a blue background are represented in our database.
When you click on an element, a new periodic table will come up.
The element you choose will then be in pink. The elements that are in blue now
represent constituents in molecules that contain the element you just chose and are in our database.
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 periodic 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.
- 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.
- Molecular Species
- This is the molecular species to which the data pertains.
the ASCII version
|P or Pi
|D or Di
- The observed transition frequency is given in megahertz.
- 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.
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 (twice the standard deviation from the fit). 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).
||Resultant total angular momentum quantum number, excluding nuclear spins.
||Rotational angular momentum quantum number, excluding electron and nuclear
spins, in the case where electron spin is present.
||Projection of J (or N) on the symmetry axis in the limiting
prolate or oblate symmetric top.|
||Resultant angular momentum quantum number including nuclear spin for one
||Resultant total angular momentum quantum number.|
||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. The vibrational state remains unchanged for nearly all transitions, so a single set of quantum numbers
- Parity is a property of a state (electronic, vibrational, etc.) or the
wavefunction describing the state as either even (+) or odd (-) character.
- 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. These additional references also include
publications which are indirectly related to the frequency measurements and
which contain intensity measurements.