利用衝擊波管研究三重態亞甲基與氫氣和氧氣的高溫反應動力學

Abstract

我們利用活塞型衝擊波管-原子共振吸收光譜(ARAS)技術來研究1800 K至2000 K溫度範圍之三重態亞甲基3CH2的反應動力學。以電腦程式模擬適解由實驗測得之碘原子、氫原子以及氧原子的濃度變化，進而得到在該反應條件下，二碘甲烷熱解之第二步驟速率常數(k3-2) 、3CH2 + H2與3CH2 + O2在高溫下的反應速率常數(k3-8與k3-12)以及反應途徑分支比。所得到的二碘甲烷熱解的速率常數Ln ( k3-2 / cm3 molecule-1 s-1 ) = - ( 17.28 ± 0.79 ) - ( 30.17 ± 1.40 ) × 103 / T這是關於二碘甲烷熱解反應所做的第一組實驗量測，在此之前，並未有實驗組進行此實驗。此次實驗所得到3CH2 + H2反應速率常數Ln ( k3-8 / cm3 molecule-1 s-1 ) = - ( 22.0 ± 1.9 ) - ( 7.8 ± 3.7 ) × 103 / T，為高溫範圍內的第一組實驗量測數據，並與本實驗室之前發表的0.48 ppm CH3OH + 1000 ppm H2熱解實驗中的理論計算值極吻合;我們亦得到CH3 + H2反應速率常數Ln ( k3-9 / cm3 molecule-1 s-1 ) = - ( 16.8 ± 2.4 ) - ( 21.0 ± 4.7 ) × 103 / T則與之前的文獻數據吻合。3CH2 + O2本研究量得之反應之速率常數為k3-12(T) = (2.84 ± 0.12) × 10-11 exp[-(755 ± 33)/T)cm3 molecule-1 s-1和Vinckier與Debruyn所報導的k3-12(T) = ( 2.2 + 1.1/-0.8 ) × 10-11 exp[(-1.5 ± 0.3) kcal mol-1/RT]經外插至高溫後相當符合本次實驗結果。有關3CH2 + O2 反應途徑，我們參照之前Moore實驗組的文獻資料結合此次實驗結果得到以下反應途徑分枝比: CO + OH + H途徑: 0.3 ，CO2 + 2H途徑:□0.15，CH2O + O途徑 :□0.3，CO2 + H2途徑 : 0.25。

A diaphramless shock tube coupled with atomic resonance absorption spectrophotometry (ARAS) was employed to study the kinetics of the reactions of triplet methylene with oxygen and hydrogen between 1800 and 2000 K. We obtained Ln ( k3-2 / cm3 molecule-1 s-1 ) = - ( 17.28 ± 0.79 ) - ( 30.17 ± 1.40 ) × 103 / T , the second step rate constants of the CH2I2 thermal decomposition , in this temperature range . This is the first experimental result reported on the CH2I2 thermal decomposition. For the reaction 3CH2 + H2 , Ln ( k3-8 / cm3 molecule-1 s-1 ) = - ( 22.0 ± 1.9 ) - ( 7.8 ± 3.7 ) × 103 / T was yielded in this study. Present experimental results are found to be consistent with the calculations from our previous work of 0.48 ppm CH3OH + 1000 ppm H2 thermal decomposition. We also determined the rate constants for CH3 + H2 reaction , Ln ( k3-9 / cm3 molecule-1 s-1 ) = - ( 16.8 ± 2.4 ) - ( 21.0 ± 4.7 ) × 103 / T , which agrees with previous references. k3-12 (T) = (2.84 ± 0.12) × 10-11 exp[-(755 ± 33)/T) cm3 molecule-1 s-1 is the total rate constant for 3CH2 +O2 determined in this study. Our results agree with that of Vinckier and Debruyn when extrapolation at high temperature. k3-12 (T) = (2.2 + 1.1/-0.8 ) × 10-11 exp[(-1.5 ± 0.3) kcal mol-1/RT] that predicted by Vinckier與Debruyn. After combining the result of this work and Moore et al. the branching fractions for this reaction were obtained as follow : CO + OH + H channel : 0.3，CO2 + 2H channel :□0.15，CH2O + O channel :□0.3，CO2 + H2 channel : 0.25 .