Department of Applied Chemistry, National Chiao Tung University, 1001, Ta Hsuch Road, Hsinchu, 30010 Taiwan.
J Phys Chem A. 2010 May 6;114(17):5493-502. doi: 10.1021/jp100535r.
H atom produced in the thermal decomposition of CH(3)OH highly diluted in Ar (0.48-10 ppm) was monitored behind reflected shock waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (+/-10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of approximately 1 x 10(11) atoms/cm(3) and enables us to determine the branching fraction for the direct H atom production channel, CH(3)OH --> CH(2)OH + H (channel 1c ) in a mixture of 1 ppm CH(3)OH. Channel 1c is confirmed to be minor, that is, branching fraction for channel 1c is expressed by Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02), which corresponds to k(1c)/k(1) < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH(3)OH with (100-1000) ppm H(2), the total decomposition rate k(1) for CH(3)OH --> products is measured from the time dependence of H atom, where the radical products of main channels 1a and 1b , that is, OH, CH(3), and CH(2), were converted rapidly into H atoms. The experimental result is summarized as Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction: (3)CH(2) + H(2) --> CH(3) + H (reaction 3 ). The rate is given by k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T(2.3) exp (-3699/T). This result is used for numerical simulations to evaluate k(1). Present experimental results on the thermal decomposition rate of CH(3)OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH(3)OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.
在固定温度（和压力）下，通过原子共振吸收光谱法（ARAS）监测在氩气中高度稀释的甲醇（0.48-10 ppm）的热分解产生的 H 原子，即 1660（1.73 atm）、1760（2.34 atm）、1860（2.04 atm）、1950（2.18 atm）和 2050 K（1.76 atm）（分别为 +/-10 K）。通过将 ARAS 信号平均到大约 1 x 10(11)原子/cm(3)的浓度，实现了对 H 原子的高灵敏度，并使我们能够确定直接 H 原子生成通道的分支分数，即 CH(3)OH --> CH(2)OH + H（通道 1c）在 1 ppm CH(3)OH 的混合物中。通道 1c 被确认为次要的，即通道 1c 的分支分数表示为 Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02)，这对应于当前温度范围内的 k(1c)/k(1) < 0.03。通过使用 0.48 和 1.0 ppm CH(3)OH 和（100-1000）ppm H(2)，从 H 原子的时间依赖性测量 CH(3)OH 的总分解速率 k(1)，其中主要通道 1a 和 1b 的自由基产物，即 OH、CH(3)和 CH(2)，迅速转化为 H 原子。实验结果总结为 Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38)。基于高精度从头算/TST 计算的理论研究已经针对反应：(3)CH(2) + H(2) --> CH(3) + H（反应 3）进行了。该速率表示为 k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T(2.3) exp (-3699/T)。该结果用于数值模拟以评估 k(1)。CH(3)OH 热分解速率的当前实验结果与以前的工作一致。还发现，通过使用由 36 个基元反应组成的反应机制，通过动力学模拟可以很好地再现 Ar 中 10 ppm CH(3)OH 中观察到的[H]的时间依赖性。
