Cyanopolyynes, H(C=C)_nC=N (n = 3-6), were formed by laser ablation of carbon particles in liquid acetonitrile. The molecules were separated according to the size n and characterized by UV absorption spectroscopy, mass spectroscopy in combination with gas-chromato-graphic separation, and nuclear magnetic resonance (NMR) spectroscopy. For the study of nascent carbon cluster distribution during the growth of the long carbon chain molecules, isotopomer distribution was analyzed by NMR spectroscopy for the product molecules. Two cyanopolyynes of HC7N and HC9N were isolated from solutions after laser ablation of isotope-enriched carbon powder (99 ~(13)C) in liquid acetonitrile, CH3CN, of natural isotopic abundance (1.1 ~(13)C). With the observed chemical shift, 8, and spin-spin coupling constants, J_(ch) and J_(cc), spectral simulation was made to determine relative abundance of possible isotopomeric forms for HC9N. We found that the isotope of ~(12)C, mostly from solvent molecules, contributes substantially for the part of carbon in the cyano group, -C=N, in HC9N. The isotopomer distribution observed for the sequence of H-C=C-C=C- was fairly explainable by a binomial, random distribution of the two carbon isotopes of ~(12)C and ~(13)C, reducing the concentration of ~(13)C to 76-55.
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