Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstrasse 12, 76131 Karlsruhe, Germany.
J Phys Chem A. 2012 Jul 12;116(27):7293-301. doi: 10.1021/jp303069g. Epub 2012 Jul 3.
Rate coefficients for the reaction (3)NCN + NO → products (R3) were measured in the temperature range 251-487 K at pressures from 10 mbar up to 50 bar with helium as the bath gas. The experiments were carried out in slow-flow reactors by using pulsed excimer laser photolysis of NCN(3) at 193 or 248 nm for the production of NCN. Pseudo-first-order conditions (NCN ≪ NO) were applied, and NCN was detected time-resolved by resonant laser-induced fluorescence excited near 329 nm. The measurements at the highest pressures yielded values of k(3) ∼ 8 × 10(-12) cm(3) s(-1) virtually independent of temperature and pressure, which indicates a substantially smaller high-pressure limiting value of k(3) than predicted in earlier works. Our experiments at pressures below 1 bar confirm the negative temperature and positive pressure dependence of the rate coefficient k(3) found in previous investigations. The falloff behavior of k(3) was rationalized by a master equation analysis based on a barrierless association step (3)NCN + NO ↔ NCNNO((2)A″) followed by a fast internal conversion NCNNO((2)A″) ↔ NCNNO((2)A'). From 251-487 K and above 30 mbar, the rate coefficient k(3) is well represented by a Troe parametrization for a recombination/dissociation reaction, k(3)(T,P) = k(4)(∞)k(4)(0)[M]F(k(4)(0)[M] + k(4)(∞))(-1), where k(4) represents the rate coefficient for the recombination reaction (3)NCN + NO. The following parameters were determined (30% estimated error of the absolute value of k(3)): k(4)(0)[M=He] = 1.91 × 10(-30)(T/300 K)(-3.3) cm(6) s(-1)[He], k(4)(∞) = 1.12 × 10(-11) exp(-23 K/T) cm(3) s(-1), and F(C) = 0.28 exp(173 K/T).
速率系数的反应 (3)NCN + 没有 → 产品 (R3) 分别在温度范围 251-487 K 压力从 10 毫巴高达 50 巴与氦气作为浴气体。实验在慢流反应堆脉冲准分子激光光解 NCN(3)在 193 或 248 nm 为生产 NCN。伪一阶条件 (NCN ≪ 没有) 是应用的，和 NCN 检测时间分辨通过共振激光诱导荧光激发附近 329 nm。在最高压力的测量值 k(3)∼ 8 × 10(-12)厘米(3) s(-1)几乎独立于温度和压力，这表明一个大大较小的高压力极限值 k(3)比预测在早期的作品。我们的实验压力低于 1 巴确认的负温度和积极的压力依赖的速率系数 k(3)发现在以前的调查。下降的行为 k(3)合理化的主方程分析基于一个无势协会一步 (3)NCN + 没有 ↔ NCNNO((2)A″)接着快速内部转换 NCNNO((2)A″) ↔ NCNNO((2)A')。从 251-487 K 和以上 30 毫巴，速率系数 k(3)是很好的代表 Troe 参数化一个重组/分解反应，k(3)(T、P) = k(4)(∞)k(4)(0)[M]F(k(4)(0)[M] + k(4)(∞))(-1)，其中 k(4)表示速率系数的重组反应 (3)NCN + 没有。以下参数确定 (30%的绝对值估计错误 k(3)): k(4)(0)[M=氦] = 1.91 × 10(-30)(T/300 K)(-3.3)厘米(6) s(-1)[氦]，k(4)(∞) = 1.12 × 10(-11)exp(-23 K/T)厘米(3) s(-1)，和 F(C) = 0.28 exp(173 K/T)。
