Surface C-H stretching features on meteoritic nanodiamonds

Abstract

Nanometre-sized diamonds (nanodiamonds) are to date the most abundant presolar grains in primitive meteorites. They are therefore presumed to be an abundant component of the dust in the interstellar medium. What then are the expected spectroscopic signatures of these grains in the interstellar medium? In order to answer this question we have examined the infrared spectroscopic properties of the nanodiamonds extracted from the Orgueil meteorite. The nanodiamonds were surface-cleaned and hydrogenated under vacuum. The spectra of the surface C-H stretching features in the 3-5 μm region were then taken. Comparison with larger synthetic nanodiamonds shows that the spectra are size-dependent. The observed meteoritic nanodiamond C-H stretching features are very different from the features seen on the surfaces of larger diamonds (sizes ≥50 nm). Less-processed Orgueil nanodiamonds appear to provide an intriguing similarity to the class B infrared emission band spectra in the 3.3-3.7 μm wavelength region. The spectra of the nanodiamond C-H stretching features can be used as a template in the search for interstellar nanodiamonds in the infrared spectra of astronomical objects. In addition the size-dependence of the nanodiamond surface C-H features can be used to place rigid and robust constraints upon the sizes of these particles in circumstellar media and in the ISM.