Smith David C, Godard Gaston
National Natural History Museum, Dept. Earth History, Lab. Extraterrestrial Materials, Case 52, 61 Rue Buffon, 75005 Paris, France.
Spectrochim Acta A Mol Biomol Spectrosc. 2009 Aug;73(3):428-35. doi: 10.1016/j.saa.2008.10.025. Epub 2008 Oct 31.
A UV laser has now been used to measure the Raman spectrum of lonsdaleite. This mineral species is a little-known hexagonal form of carbon having no known P-T field of stability. Lonsdaleite is known to coexist with diamond and/or graphite in certain impact structures and meteorites. Its presence in microinclusions in some ultrahigh-pressure eclogites is under discussion as there is a considerable wavenumber overlap of the sp(3) Raman band of lonsdaleite in the 1200-1400 cm(-1) region with certain bands of haematite, graphite and diamond, and also with "disordered-diamond" having a downshifted wavenumber. Various incoherent previously published values of the Raman bands are briefly reviewed and an attempt is made to establish a reference spectrum. Four samples of lonsdaleite from the Zapadnaya and Popigai impact structures (Ukraine) were measured with three different laser sources (488, 514.5 and 325 nm) with two Raman spectrometers. UV-Raman was less fluorescent. All the new data were coherent in establishing an sp(3) band centred at 1324+/-4 cm(-1) with a FWHM about five times wider than that of diamond and an intensity about 500 times weaker. The presence of a second band giving a weak shoulder around 1225 cm(-1) is discussed with respect to the alternative of one continuous asymmetrical band.
紫外激光现已用于测量六方金刚石的拉曼光谱。这种矿物是一种鲜为人知的六方碳形式，其稳定的压力-温度范围未知。已知六方金刚石在某些撞击构造和陨石中与金刚石和/或石墨共存。由于六方金刚石在1200 - 1400 cm⁻¹区域的sp(3)拉曼谱带与赤铁矿、石墨和金刚石的某些谱带以及波数下移的“无序金刚石”有相当大的波数重叠，因此其在一些超高压榴辉岩微包裹体中的存在仍在讨论中。本文简要回顾了先前发表的各种非相干的拉曼谱带值，并尝试建立一个参考光谱。使用两台拉曼光谱仪，用三种不同的激光源（488、514.5和325 nm）对来自扎帕德尼亚和波皮盖撞击构造（乌克兰）的四个六方金刚石样品进行了测量。紫外拉曼的荧光较弱。所有新数据在确定一个以1324±4 cm⁻¹为中心的sp(3)谱带方面是一致的，其半高宽约为金刚石的五倍，强度约为金刚石的五百分之一。针对一个连续不对称谱带的可能性，讨论了在1225 cm⁻¹左右出现第二个给出弱肩峰的谱带的情况。
