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Title: Post-transition state dynamics and product energy partitioning following thermal excitation of the F∙∙∙HCH 2 CN transition state: Disagreement with experiment

Born-Oppenheimer direct dynamics simulations were performed to study atomistic details of the F + CH 3CN → HF + CH 2CN H-atom abstraction reaction. The simulation trajectories were calculated with a combined M06-2X/MP2 algorithm utilizing the 6-311++G** basis set. In accord with experiment and assuming the accuracy of transition state theory (TST), the trajectories were initiated at the F-HCH 2CN abstraction TS with a 300 K Boltzmann distribution of energy and directed towards products. Recrossing of the TS was negligible, confirming the accuracy of TST for the simulation. HF formation was rapid, occurring within 0.014 ps of the trajectory initiation. The intrinsic reaction coordinate (IRC) for reaction involves rotation of HF about CH 2CN and then trapping in the CH 2CN-HF post-reaction potential energy well of ~10 kcal/mol with respect to the HF + CH 2CN products. In contrast to this IRC, five different trajectory types were observed, with the majority involving direct dissociation and only 11% approximately following the IRC. The HF vibrational and rotational quantum numbers, n and J, were calculated when HF was initially formed and they increase as potential energy is released in forming the HF + CH 2CN products. The population of the HF productmore » vibrational states is only in qualitative agreement with experiment, with the simulations showing depressed and enhanced populations of the n = 1 and 2 states as compared to experiment. From the simulations and with an anharmonic zero-point energy constraint, the percentage partitioning of the product energy to relative translation, HF rotation, HF vibration, CH 2CN rotation and CH 2CN vibration is 5, 11, 60, 7, and 16%, respectively. In contrast the experimental energy partitioning percentages to HF rotation and vibration are 6 and 41%. Comparisons are made between the current simulation and those for other F + H-atom abstraction reactions. The simulation product energy partitioning and HF vibrational population for F + CH 3CN → HF + CH 2CN are similar to those for these other reactions. Finally, a detailed discussion is given of possible origins of the difference between the simulation and experimental energy partitioning dynamics for the F + CH 3CN → HF + CH 2CN reaction. The F + CH 3CN reaction also forms the CH 3C(F)N intermediate, in which the F-atom adds to the C≡N bond. However, this intermediate and the F---CH 3CN and CH 3CN-F van der Waals complexes are not expected to affect the F + CH 3CN → HF + CH 2CN product energy partitioning.« less
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  1. Texas Tech Univ., Lubbock, TX (United States). Dept. of Chemistry and Biochemistry
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Division
  3. Texas Tech Univ., Lubbock, TX (United States). Dept. of Chemistry and Biochemistry; Tianjin Univ., Tianjin (China). School of Pharmaceutical Science and Technology; Univ. of Natural Resources and Life Sciences Vienna, Vienna (Austria). Inst. for Soil Research
  4. Univ. of Natural Resources and Life Sciences Vienna, Vienna (Austria). Inst. for Soil Research
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 147; Journal Issue: 14; Journal ID: ISSN 0021-9606
American Institute of Physics (AIP)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science - Office of Basic Energy Sciences - Chemical Sciences, Geosciences, and Biosciences Division; Welch Foundation; Texas Tech University; University of Texas - Austin - Texas Advanced Computing Center; USDOE
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Active Thermochemical Tables; Chemical reaction; Dynamics; Energy partitioning; Thermochemistry; Transition State; Transition State Theory
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1398823