The origin of diamonds in meteorites on the basis of Raman spectra.

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We measured Raman spectra of various diamonds and the full width at half maximum(FWHM)and wavenumber position of a Raman line near 1332 cm^<-1> are compared to better understand the origin of FWHM(2-4 cm^<-1>)like the diamonds from the earth. The FWHMs of Raman peaks of the shock-produced diamonds are largely deviated(10-120 cm^<-1>)and the peak position is significantly shifted to smaller wavenumber up to 1314 cm^<-1>. The FWHM of CVD diamonds ranges from 3 to 25 cm^<-1> and the peak position ranges from 1340 to 1328 cm^<-1>. The peak position of ureilite diamonds ranges from 1334 to 1328 cm^<-1>,which is scattered compared with the diamonds synthesized under static high pressure. The FWHM of ureilites diamonds ranges from 3 to 15 cm^<-1>,which is larger than that of the diamonds synthesized under static high pressure but is smaller than that of the shock-produced diamonds.The peak positions of some ureilite diamonds are shifted to smaller wavenumber,probably due to lonsdaleite(hexagonal diamond). The FWHM of ureilite diamonds is closer to that of CVD diamonds and evidently smaller than that of the shock-produced diamonds. Our results suggest that ureilite diamonds formed from vapor in the primitive solar nebula by chemical vapor deposition. Since duration of shock pressure caused by impact between planetary bodies is longer than that by laboratory experiments,crystallinity of shock-produced diamonds by planetary scale collisions may be improved during longer duration of shock pressure. This may cause a smaller value of the FWHM of the Raman line of diamondSingle-crystal X ray diffraction study with the Laue method using synchrotron radiation showed that a CVD diamond is polycrystalline and disordered and that the cell constant is slightly larger compared with natural diamond.Precise measurement of the peak position of Raman lines of gives information on the residual stress in minerals.