Study on Raman Spectrum Characteristics of Amber

In recent years,authenticity identification and origin identification of ambers are becoming a hot topic in the academic research field.Scholars both at home and abroad make use of Fourier transform infrared spectroscopy(FTIR)to determine the amber authenticity and origin.Raman spectrum is considered to be a useful supplement of FTIR.The authors selectively collect different varieties of amber samples from three major producing areas in the world,the Baltic Sea,Dominica and Myanmar.With the help of laser Raman spectrometer,peak positions,peak shapes and relative strength characteristics of Raman spectra and their vibration patterns are described,mainly in the range of 3 200-400cm^-1.Some molecular groups are analyzed such as vibration of C-H and C-O.The Raman spectra of amber samples from the same origin are compared and analyzed to find out their similar features,while the Raman spectra of amber samples from different origins are compared and analyzed to find out their discriminative features.The result clearly shows that the vibration of carbon chain frame in the molecular structure of amber is the main formation factor of Raman spectrum.The features of peaks in the Raman spectra of different varieties of ambers from the same producing area are almost the same.The golden amber,foamy amber and cloudy amber from Baltic Sea have similar Raman spectrum.The Dominican golden amber has the same Raman spectrum with the blue amber and the Raman spectra of golden amber,blood amber and brown red amber from Myanmar are consistent.The Raman spectra of ambers from different producing areas only have slight differences in the Raman shift.Comparing with Raman spectra of ambers from the Baltic Sea,Myanmar and Dominica,Raman spectra of the Dominican ambers have some differences in the range of 1 700-1 400cm^-1 and the Raman shift of Burmese amber below 1 200cm^-1 has significantly fewer spectral peaks as well as less absorption intensity.The previous arguments and initial assumptions put forward that using intensity ratio of ν(C=C)and δ(CH₂)(N=I₁₄₅₀cm_-1/I_1645cm-1)could determine the natural maturity of resin.The authors confirm that the value of Ncan react the change of the relative quantity of unsaturated carbon functional groups and saturated carbon functional groups in the amber internal structure as well as detect the status of the crosslinking polymerization.However,the value of N could not be the only indicative evidence for origin identification,since the Burmese amber has a lower value of N,while the Nvalues of the Baltic ambers and the Dominican ambers are close.