217.5 nanometer absorption feature in the spectrum of small silicate particles

Laboratory spectra of fine partially hydrogenated amorphous Mg2SiO4 particles have been shown to exhibit an absorption feature at 217.5 nm that matches the interstellar extinction band at this wavelength. This absorption appears to be due to an electronic transition of OH(-) ions in sites of low coordination. Absorption occurs at a similar wavelength in Fe silicates as well as in silicates of mixed Mg, Fe composition, although the best fit to the observed 217.5-nm profile is obtained with silicates containing little iron. 28 references