The Atomic Spectra Database (ASD) contains data for radiative transitions and energy levels in atoms and atomic ions. Data are included for observed transitions and energy levels of most of the known chemical elements. The links above provide access to the current lists of Holdings for Spectral Line and Energy Level Data. ASD contains data on spectral lines with wavelengths from about 20 pm (picometers) to 60 m (meters). For many lines, ASD includes radiative transition probabilities. The energy level data include the ground states and ionization energies for all spectra. Except where noted, the data have been critically evaluated by NIST.
For most spectra, wavelengths, transition-probabilities, relative intensities, and energy levels are integrated, so that all the available information for a given transition is incorporated under a single listing. For classified lines, in addition to the observed wavelength, ASD includes the Ritz wavelength, which is the wavelength derived from the energy levels. The Ritz wavelengths are usually more precise than the observed ones.
Line lists containing classified lines can be ordered by either multiplet (for a given spectrum) or wavelength. For some spectra, ASD includes lists of prominent lines with wavelengths and relative intensities but without energy-level classifications.
The contents of ASD are limited to data that have been critically compiled by NIST, or, for a few spectra compiled by R.L. Kelly, published in the Journal of Physical and Chemical Reference Data for NIST. In this sense we include only NIST "Standard Reference Data." In the case of transition probabilities, for example, this means that the listed values are estimated by NIST to have the accuracy assigned to each transition. In the case of energies and wavelengths, ASD contains critically evaluated uncertainties for a large part of all data, and they are reported in the output pages. For those data that do not have an explicit information about their uncertainty, it is implied by the number of significant figures. Uncertainties of about 90 % of ASD data are in the range from 2.5 to 25 units of the least significant decimal place of the value. Thus, most of the data in ASD are of known or estimated accuracy. In some cases, this limitation to NIST-evaluated data means that the data do not reflect the most current or accurate values, because NIST evaluations have not been performed sufficiently recently to include them.
Citations for the compilations and literature sources contained therein are provided in two ways. First, the primary sources of the listed data are summarized at the top of the output pages. Second, each listed data element is accompanied by a link to a complete bibliographic reference, which is stored in the integrated Bibliography Databases.
Each page of the ASD database (except the ASD home page) includes a menu bar displayed at the top of the page, which can be used to navigate through the database. The database includes a variety of output options and search criteria.