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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >High temperature shock tube and theoretical studies on the thermal decomposition of dimethyl carbonate and its bimolecular reactions with H and D-atoms
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High temperature shock tube and theoretical studies on the thermal decomposition of dimethyl carbonate and its bimolecular reactions with H and D-atoms

机译：高温冲击管及碳酸二甲酯热分解及其与H和D原子的双分子反应的理论研究

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摘要

The shock tube technique was used to study the high temperature thermal decomposition of dimethyl carbonate, CH_3OC(O)OCH_3 (DMC). The formation of H-atoms was measured behind reflected shock waves by using atomic resonance absorption spectrometry (ARAS). The experiments span a T-range of 1053-1157 K at pressures ～0.5 atm. The H-atom profiles were simulated using a detailed chemical kinetic mechanism for DMC thermal decomposition. Simulations indicate that the formation of H-atoms is sensitive to the rate constants for the energetically lowest-lying bond fission channel, CH_3OC(O)OCH_3 → CH_3 + CH_3OC(O)O [A], where H-atoms form instantaneously at high temperatures from the sequence of radical β-scissions, CH_3OC(O)O → CH_3O + CO_2 → H + CH_2O + CO_2. A master equation analysis was performed using CCSD(T)/cc-pv∞z//M06-2X/cc-pvtz energetics and molecular properties for all thermal decomposition processes in DMC. The theoretical predictions were found to be in good agreement with the present experimentally derived rate constants for the bond fission channel (A). The theoretically derived rate constants for this important bond-fission process in DMC can be represented by a modified Arrhenius expression at 0.5 atm over the T-range 1000-2000 K as, kA(T) = 6.85 × 10~(98)T ~(-24.239) exp(-65250 K/T) s~(-1). The H-atom temporal profiles at long times show only minor sensitivity to the abstraction reaction, H + CH_3OC(O)OCH_3 → H2 + CH_3OC(O) OCH2 [B]. However, H + DMC is an important fuel destruction reaction at high temperatures. Consequently, measurements of D-atom profiles using D-ARAS allowed unambiguous rate constant measurements for the deuterated analog of reaction B, D + CH_3OC(O)OCH_3 → HD + CH_3OC(O)OCH2 [C]. Reaction C is a surrogate for H + DMC since the theoretically predicted kinetic isotope effect at high temperatures (1000 - 2000K) is close to unity, kC ≈ 1.2 kB. TST calculations employing CCSD(T)/cc-pv∞z//M06-2X/cc-pvtz energetics and molecular properties for reactions B and C are in good agreement with the experimental rate constants. The theoretical rate constants for these bimolecular processes can be represented by modified Arrhenius expressions over the T-range 500-2000 K as, k_B(T) = 1.45 × 10 ~(-19T2.827) exp(-3398 K/T) cm~3 molecule ~(-1) s~(-1) and k_C(T) = 2.94 × 10~(-19T2.729) exp(-3215 K/T) cm~3 molecule ~(-1) s~(-1).
机译：冲击管技术用于研究碳酸二甲酯CH_3OC（O）OCH_3（DMC）的高温热分解。通过使用原子共振吸收光谱法（ARAS）在反射的冲击波后面测量H原子的形成。实验在〜0.5 atm的压力下跨度为1053-1157 K的T范围。使用详细的DMC热分解的化学动力学机理模拟H原子分布。模拟表明，H原子的形成对能量最低的键裂变通道CH_3OC（O）OCH_3→CH_3 + CH_3OC（O）O [A]的速率常数敏感，其中H原子在高温下瞬间形成自由基β-断续序列的温度CH_3OC（O）O→CH_3O + CO_2→H + CH_2O + CO_2。对于DMC中的所有热分解过程，使用CCSD（T）/cc-pv∞z// M06-2X / cc-pvtz能量学和分子性质进行了主方程分析。发现理论预测与键裂变通道（A）的当前实验得出的速率常数非常吻合。 DMC中这个重要的键裂变过程的理论推导速率常数可以通过在1000-2000 K的T范围内以0.5 atm的修正的Arrhenius表达式表示，例如kA（T）= 6.85×10〜（98）T〜 （-24.239）exp（-65250 K / T）s〜（-1）。长时间的H原子时间分布对抽象反应H + CH_3OC（O）OCH_3→H2 + CH_3OC（O）OCH2仅显示较小的敏感性[B]。但是，H + DMC是高温下重要的燃料破坏反应。因此，使用D-ARAS进行D原子分布图测量可对反应B的氘代类似物D + CH_3OC（O）OCH_3→HD + CH_3OC（O）OCH2 [C]进行明确的速率常数测量。反应C是H + DMC的替代物，因为理论上预测的高温（1000-2000K）动力学同位素效应接近统一，kC≈1.2 kB。使用CCSD（T）/cc-pv∞z// M06-2X / cc-pvtz能量学和反应B和C的分子性质进行的TST计算与实验速率常数非常吻合。这些双分子过程的理论速率常数可以通过在500-2000 K的T范围内修改的Arrhenius表达式来表示，例如k_B（T）= 1.45×10〜（-19T2.827）exp（-3398 K / T）cm 〜3分子〜（-1）s〜（-1）和k_C（T）= 2.94×10〜（-19T2.729）exp（-3215 K / T）cm〜3分子〜（-1）s〜（ -1）。

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