三大产地(波罗的海、多米尼加和缅甸)琥珀红外光谱鉴别特征

Infrared Spectral Characteristics of Ambers from Three Main Sources(Baltic,Dominica and Myanmar)

采用镜面反射法和溴化钾压片透射法对波罗的海、多米尼加和缅甸琥珀进行红外光谱测试,获得了不同产地的红外光谱鉴别特征。经仔细分析认为,尽管不同产地琥珀的红外光谱具有共同特征,但某些吸收峰位置或相对强度仍存在差异。3 000～2 800cm^-1范围内,波罗的海琥珀有两个明显的吸收峰和一个弱肩峰,多米尼加琥珀有两个吸收峰,缅甸琥珀具有三个特征吸收峰;1 740～1 690cm^-1范围内,波罗的海琥珀出现1 732cm^-1附近强吸收峰,多尼米加和缅甸琥珀有两个吸收峰,分别位于1 730和1 695cm^-1附近,但是多米尼加琥珀1 730cm^-1峰强度小于1 695cm^-1,与缅甸琥珀相反;1 300～1 000cm^-1范围内,波罗的海琥珀具有典型的＂波罗的海肩峰＂及1 163cm^-1附近的强吸收,多米尼加琥珀出现1 240cm^-1附近吸收峰,缅甸琥珀在此范围内的强吸收峰组成＂山＂字型;波罗的海琥珀R（A1 381cm^-1/A1 456cm^-1）值约为0.9,多米尼加琥珀约0.8,而缅甸为0.7。上述差异可以作为判断琥珀产地的鉴别依据。不同产地琥珀的红外光谱出现差异,可能与其形成年代、植物种源和地质环境不同有关。根据红外光谱中与环外C=C双键有关的吸收峰的存在和强度,推断三个产地的琥珀形成时间由早到晚分别为缅甸、波罗的海、多米尼加。红外光谱在识别琥珀产地方面具有重要的宝石学意义,同时在考古学研究与应用中有潜在意义。

Infrared spectra of ambers from Baltic,Dominica and Myanmar are obtained by Specular Reflection and KBr Pellet Transmission Methods.Although the infrared spectra of these ambers present similar features for ambers from different locations,refined differences in location and intensity of absorption peaks could be identified among them.Between 3 000 and 2 800cm^-1,two obvious bands with a weak shoulder peak are seen in the Baltic amber spectrum,whereas there are two bands in the Dominica＇s and three bands in the Myanmar＇s.In region of 1 740～1 690cm^-1,one band appears at 1 732cm^-1 in the spectra of the Baltic amber sample,distinctly different from those of the Dominican and Myanmar ambers which have a doublet at 1 730 and 1 695cm^-1.For the Dominican amber,the intensity of 1 730cm^-1 is much stronger than that of 1 695cm^-1,being contrary to the spectra of the Myanmar amber,whose intensity of 1 730cm^-1 is weaker than that of 1 695cm^-1.Within region of 1 300～1 000cm^-1,Baltic amber can be distinguished from other two origin ambers by a horizontal shoulder,often called ＂Baltic shoulder＂,with a definite band at 1 163cm^-1.Spectra of the Dominican amber show a unique band at 1 240cm^-1,while spectra of the Myanmar amber have a triplet at 1 224,1 130 or 1 154cm^-1 and 1 033cm^-1,like＂wave of mountain＂altogether.Ratios of absorption intensity of 1 381 vs.1 456cm^-1 are about 0.9,0.8and 0.7respectively for the Baltic,Dominican and Myanmar ambers.These differences of absorption spectra could be used as the identifiable characteristics corresponding to the ambers locality.The correlation between the ambers＇ infrared spectra and localities is probably due to their age,plant provenance and geological environment indivadually.On the basis of presence and intensity of the bands attributed to exocyclic methylene groups,it is suggested that the Myanmar amber formed earliest,followed by Baltic and then the youngest Dominican.These finding reveals that infrared spectroscopy may have significance for identifing amber locality,and thus potentially have archeological implications in determining source of some ancient ambers.