is a freely available collection of spectra, covering hundreds of thousands of organic, and inorganic compounds. Spectra include proton NMR, NMR, , transmission IR, Raman, UV-VIS and mass spectra, plus basic property data, though not all spectra types are available for all compounds. Peak assignments are available for NMR spectra. The collection may be searched by chemical name, CAS Registry Number or key. Only one spectrum may be displayed at a time. Note that (free) registration is required, and there are frequent advertisements displayed for the database producer, .