Isotope Identification Mechanisms Enabled by Swept-Wavelength Raman Spectroscopy.

Swept-wavelength Raman signatures have been measured for isotopic variants of polyethylene, acetic acid, and potassium sulfates. The swept-wavelength measurements produce two-dimensional Raman signatures which enable identification techniques based on changes in Raman peak amplitudes as a function of wavelength. In addition to the typical Raman peak energy shifts, which results from the change in isotope mass, three wavelength dependent mechanisms for isotope identification have been identified. Changes in the shape of the Raman signal, the presence and absence of Raman peaks over specific wavelength ranges, and changes in absorption of the Raman signal were observed as a result of isotopic substitution. These features provide additional specificity in the isotopic Raman signatures which suggests swept-wavelength Raman signatures will facilitate the identification of isotopes in complex and dirty mixtures. Measurements in the visible range suggest that the identification mechanisms are primarily evident in the ultraviolet, or resonance Raman, region.