Laser ablation molecular isotopic spectrometry of carbon isotopes

Quantitative determination of carbon isotopes using Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is described. Optical emission of diatomic molecules CN and C-2 is used in these measurements. Two quantification approaches are presented: empirical calibration of spectra using a set of reference standards and numerical fitting of a simulated spectrum to the experimental one. Formation mechanisms of C-2 and CN in laser ablation plasma are briefly reviewed to provide insights for implementation of LAMIS measurements. A simulated spectrum of the C-12(2) Swan system was synthesized using four constituents within 473.5-476.5 nm. Simulation included three branches of C-12(2) (1-0), branches R(0-0) and R(1-1), and branch P(9-8) of C-12(2). Spectral positions of the tail lines in R(0-0) and R(1-1) were experimentally measured, since they were not accurately known before. The Swan band (1-0) of the isotopologue (CC)-C-13-C-12 was also simulated. Fitting to the experimental spectrum yielded the ratio C-13/C-12 = 1.08% in a good agreement with measurements by isotope ratio mass spectrometry. LAIVIIS promises to be useful in coal, oil and shale exploration, carbon sequestration monitoring, and agronomy studies. (C) 2015 Elsevier B.V. All rights reserved.