Laser Ablation Molecular Isotopic Spectrometry (LAMIS) was recently reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. With 13 C-labelled benzoic acid as a model sample, this research utilized the LAMIS approach to clarify the formation mechanisms of C 2 and CN molecules during laser ablation of organic materials. Because the isotopic ratios in the molecular bands could deviate from statistical distribution depending on their formation pathways, the dominant mechanism can be identified through a comparison of the experimental observed isotopic patterns in the molecular emission with the theoretical statistical pattern. For C 2 formation, the experimental 12 C 12 C / 13 C 12 C ratios support a recombination mechanism through atomic carbon at early delay time but also indicate the presence of other operating mechanisms as the plasma evolves; it is proposed that some of the C 2 molecules are released directly from the aromatic ring of the sample as molecular fragments. In contrast, the temporal profiles in the 12 C / 13 C ratios derived from CN emission exhibited opposite behavior with those derived from C 2 emission, which unambiguously refutes mechanisms that require C 2 as a precursor for CN formation; CN formation likely involves atomic carbon or species with a single carbon atom.

Laser ablation molecular isotopic spectrometry (LAMIS) recently was reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. This research utilized the LAMIS approach to study C2 molecular formation from laser ablation of carbon isotopic samples in a neon gas environment at 0.1 MPa. The isotopic shift for the Swan system of the C2 Δν = 1 band was chosen for carbon isotope analysis. Temporal and spatial resolved measurements of (12)C2, (12)C(13)C, and (13)C2 show that C2 forms from recombination reactions in the plasma. A theoretical simulation was used to determine the temperature from the molecular bands and to extract the isotopic ratio of (12)C/(13)C derived from (12)C2, (12)C(13)C, and (13)C2. Our data show that the ratio of (12)C/(13)C varies with time after the laser pulse and with distance above the sample. (12)C/(13)C deviates from the nominal ratio (2:1) at early times and closest to the sample surface. These measurements provide understanding of the chemical processes in the laser plasma and analytical improvement using LAMIS.