Leiden Atomic and Molecular Database
Data format | RADEX

The aim of this project is to provide users of radiative transfer codes with the basic atomic and molecular data needed for the excitation calculation. Line data of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are in some cases extrapolated to higher energies.

Currently the database contains data for 4 atomic / ionic and 36 molecular species. In addition, several isotopomers and deuterated versions are available, usually via the page for the main species. Work is currently underway to add more datafiles. We encourage comments from the users in order to improve and extend the database.

This database should form an important tool in analyzing observations from current and future infrared and (sub)millimetre telescopes. Databases such as these rely heavily on the efforts by the chemical physics community to provide the relevant atomic and molecular data. We strongly encourage further efforts in this direction, so that data for more species become available and the current extrapolations of collisional rate coefficients can be replaced by actual calculations in future releases.

RADEX, a computer program for performing statistical equilibrium calculations is made publically available as part of the data base. The program comes in 2 versions: an on-line calculator for quick checks, and a stand-alone version for extensive calculations. For publication-quality results, always use the stand-alone version.

For new or changed datafiles, see the update history or follow us on Twitter.

If you use the data files in your work please refer to the publication by Schöier, F.L., van der Tak, F.F.S., van Dishoeck E.F., Black, J.H. 2005, A&A 432, 369-379 introducing this data base. Please mention the date when you accessed the database, in case questions arise about different versions of datafiles. When individual molecules are considered, we strongly suggest that you also refer to the original papers providing the spectroscopic and collisional data.

For a 2011 review of radiative transfer and molecular data for astrophysics and astrochemistry, see this paper.

For a 2013 review of how to compute collisional cross-sections and rate coefficients for interstellar molecules, see here.

For a Spring 2020 review of the current status and future plans of LAMDA, see here.

This website is dedicated to Fredrik Schöier, who initiated this database. Unfortunately, Fredrik passed away on 14 January 2011, at the age of 41. We remember Fredrik as a dedicated and inspiring scientist. See also this obituary.

Floris van der Tak, Ewine van Dishoeck, John Black

The LAMDA database is supported by the Netherlands Organization for Scientific Research (NWO), the Netherlands Research School for Astronomy (NOVA), and the Swedish Research Council.

Send comments to