Poster Presentations
Day 3, June 12（Fri.） Room P (5F 501+502)
- 3P-13
Theoretical Prediction of n-Heptane Field Ionization Mass Spectrum by Quantum Chemical Calculation and Reaction Kinetics Analysis towards Automated Structural Elucidation of Unknown Environmental Contaminants
(1Kagoshima Univ., 2Yokohama City Univ.)
oHirokazu Takanashi1, Mitsuo Takayama2, Ibuki Oda1, Tsunenori Nakajima1
A proof-of-principle study for automated structural elucidation of unknown environmental contaminants is reported, integrating quantum chemical calculations with reaction rate analyses. In this approach, the isomer whose predicted mass spectrum best matches the experimental spectrum is proposed as the most probable structure. The method was demonstrated using the FI mass spectrum of n-heptane as a model system. Starting from a stable conformation, the SC-AFIR method was employed to systematically explore the fragmentation pathway network, resulting in 976 stable structures, 1,899 transition states, and 1,897 fragmentation pathways. Additional pathways may be identified with ongoing calculations. Fragmentation pathways for all five stable fragment ions observed in the experimental spectrum were elucidated, with 6 to 72 pathways identified per ion. For each ion, the pathway with the lowest energy barrier was selected, and reaction rate constants were calculated using QET. Assuming an internal energy of 1.1 eV, the predicted mass spectrum showed good agreement with experiment. Ions resulting from higher-barrier pathways predicted by quantum chemical calculations were not observed experimentally, while those from lower-barrier pathways were. Although further calculation and methodological improvements are needed, these results demonstrate the fundamental feasibility of predicting mass spectra based on quantum chemical calculations and reaction rate analyses.