Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.
J Phys Chem A. 2011 Dec 22;115(50):14382-90. doi: 10.1021/jp208715c. Epub 2011 Nov 30.
The high-temperature rate constants of the reactions NCN + NO and NCN + NO(2) have been directly measured behind shock waves under pseudo-first-order conditions. NCN has been generated by the pyrolysis of cyanogen azide (NCN(3)) and quantitatively detected by sensitive difference amplification laser absorption spectroscopy at a wavelength of 329.1302 nm. The NCN(3) decomposition initially yields electronically excited (1)NCN radicals, which are subsequently transformed to the triplet ground state by collision-induced intersystem crossing (CIISC). CIISC efficiencies were found to increase in the order of Ar < NO(2) < NO as the collision gases. The rate constants of the NCN + NO/NO(2) reactions can be expressed as k(NCN+NO)/(cm(3) mol(-1)s(-1)) = 1.9 × 10(12) exp[-26.3 (kJ/mol)/RT] (±7%,ΔE(a) = ± 1.6 kJ/mol, 764 K < T < 1944 K) and k(NCN+NO(2))/(cm(3) mol(-1)s(-1)) = 4.7 × 10(12) exp[-38.0(kJ/mol)/RT] (±19%,ΔE(a) = ± 3.8 kJ/mol, 704 K < T < 1659 K). In striking contrast to reported low-temperature measurements, which are dominated by recombination processes, both reaction rates show a positive temperature dependence and are independent of the total density (1.7 × 10(-6) mol/cm(3) < ρ < 7.6 × 10(-6) mol/cm(3)). For both reactions, the minima of the total rate constants occur at temperatures below 700 K, showing that, at combustion-relevant temperatures, the overall reactions are dominated by direct or indirect abstraction pathways according to NCN + NO → CN + N(2)O and NCN + NO(2) → NCNO + NO.
NCN + NO 和 NCN + NO（2）反应的高温速率常数已在准一级条件下通过激波后直接测量。NCN 通过三聚氰酸亚硝酰胺（NCN（3））的热解产生，并通过灵敏的差分放大激光吸收光谱在 329.1302nm 波长处定量检测。NCN（3）分解最初产生电子激发的（1）NCN 自由基，随后通过碰撞诱导系间交叉（CIISC）转化为三重态基态。发现 CIISC 效率按 Ar <NO（2）<NO 的顺序增加，作为碰撞气体。NCN + NO/NO（2）反应的速率常数可表示为 k（NCN+NO）/（cm（3）mol（-1）s（-1））= 1.9×10（12）exp[-26.3（kJ/mol）/RT]（±7%，ΔE（a）=±1.6 kJ/mol，764 K < T < 1944 K）和 k（NCN+NO（2））/（cm（3）mol（-1）s（-1））= 4.7×10（12）exp[-38.0（kJ/mol）/RT]（±19%，ΔE（a）=±3.8 kJ/mol，704 K < T < 1659 K）。与报告的低温测量形成鲜明对比的是，这些低温测量主要由重组过程主导，两种反应速率都表现出正温度依赖性，并且与总密度无关（1.7×10（-6）mol/cm（3）<ρ<7.6×10（-6）mol/cm（3））。对于这两种反应，总速率常数的最小值出现在 700K 以下的温度下，表明在与燃烧相关的温度下，整体反应主要由直接或间接的抽提途径主导，根据 NCN + NO → CN + N（2）O 和 NCN + NO（2）→ NCNO + NO。
