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

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 3000 and 2800 cm(-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 1740~1690 cm(-1), one band appears at 1732 cm(-1) in the spectra of the Baltic amber sample, distinctly different from those of the Dominican and Myanmar ambers which have a doublet at 1730 and 1695 cm(-1). For the Dominican amber, the intensity of 1730 cm(-1) is much stronger than that of 1695 cm(-1), being contrary to the spectra of the Myanmar amber, whose intensity of 1730 cm(-1) is weaker than that of 1695 cm(-1). Within region of 1300~1000 cm(-1), Baltic amber can be distinguished from other two origin ambers by a horizontal shoulder, often called "Baltic shoulder", with a definite band at 1163 cm(-1). Spectra of the Dominican amber show a unique band at 1240 cm(-1), while spectra of the Myanmar amber have a triplet at 1224, 1130 or 1154 cm(-1) and 1033 cm(-1), like "wave of mountain" altogether. Ratios of absorption intensity of 1381 vs. 1456 cm(-1) are about 0.9, 0.8 and 0.7 respectively 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.