Raman frequencies of graphitic carbon in Antarctic ureilites

Abstract

Raman frequencies for the in-plane lattice vibration of graphite were surveyed for four Antarctic ureilites in order to construct a paradigm for structural properties of graphitic carbon in ureilites. Raman spectra were obtained by point-by-point measurements using a laser microbeam 1μm in diameter. The measured results formed an array in a two-dimensional plot between the E_ frequency and intensity ratio of two graphite-derived Raman bands. The graphitic matter in ALH-78019 gave the averaged E_ frequency at 1582.0 ⊿cm^, which agrees with the well-established wavenumber of the E_ in-plane lattice vibration of graphite. On the contrary, some graphitic matter in the ureilites (ALH-77257,Y-791538 and MET-78008) exhibited considerably up-shifted E_ frequency. Distribution in the array was proved to be closely linked to the extent of shock which the ureilites suffered