The Online Detection of Carbon Isotope by Laser-induced Breakdown Spectroscopy
The study of carbon cycle is profound to the global ecosystem. In this paper, the isotopic spectroscopy based on laser-induced breakdown spectroscopy (LIBS) technique was applied to the online detection of carbon isotope and the study of atmospheric carbon cycle. The emission of carbon dioxide in atmosphere was simulated by using laser beam to ablate the coal, wood and paper samples. The emission spectra of smoke show that the carbon dioxide in smoke can be online detected by the analysis of molecular spectrum of CN radical. Then, taking the urea as carbon isotope samples, the isotopic shifts of the CN molecular spectra were observed obviously. The emission band of the transition (1,0) redshifts for about 0.6 nm while the emission band of the transition (0,1) blueshifts for about 0.8 nm. What’s more, the gaseous 13CO2 was directly detected by LIBS and the isotopic shifts of CN bands from CO2 were also measured. Moreover, the energy differences of the isotopic shifts of CN emission band were calculated based on density functional theory with the B3PW91/6-31+G(d) basis set, and the calculation results were basically consistent with the experimental values. Finally, the wavelength shifts of all the six different combinations of carbon and nitrogen isotopes were calculated. All the results indicate that the LIBS technique combined with isotope spectrum is a promising and effective online detection method of gaseous carbon isotope.