Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling

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• 作者：Anna Busch ; N煤ria Gonz谩lez-Garc铆a ; Gy枚rgy Lendvay ; Matthias Olzmann
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：July 16, 2015
• 年：2015
• 卷：119
• 期：28
• 页码：7838-7846
• 全文大小：376K
• ISSN：1520-5215

文摘

The thermal decomposition of cyanonitrene, NCN, was studied behind reflected shock waves in the temperature range 1790鈥?960 K at pressures near 1 and 4 bar. Highly diluted mixtures of NCN₃ in argon were shock-heated to produce NCN, and concentration鈥搕ime profiles of C atoms as reaction product were monitored with atomic resonance absorption spectroscopy at 156.1 nm. Calibration was performed with methane pyrolysis experiments. Rate coefficients for the reaction ³NCN + M 鈫?³C + N₂ + M (R1) were determined from the initial slopes of the C atom concentration鈥搕ime profiles. Reaction R1 was found to be in the low-pressure regime at the conditions of the experiments. The temperature dependence of the bimolecular rate coefficient can be expressed with the following Arrhenius equation: k₁^bim = (4.2 卤 2.1) 脳 10¹⁴ exp[鈭?42.3 kJ mol^鈥?/(RT)] cm³ mol^鈥? s^鈥?. The rate coefficients were analyzed by using a master equation with specific rate coefficients from RRKM theory. The necessary molecular data and energies were calculated with quantum chemical methods up to the CCSD(T)/CBS//CCSD/cc-pVTZ level of theory. From the topography of the potential energy surface, it follows that reaction R1 proceeds via isomerization of NCN to CNN and subsequent C鈥揘 bond fission along a collinear reaction coordinate without a tight transition state. The calculations reproduce the magnitude and temperature dependence of the rate coefficient and confirm that reaction R1 is in the low-pressure regime under our experimental conditions.