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. ASD contains data on spectral lines with wavelengths from about 0.2 Å (ångströms) 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.