A shock-tube, laser-schlieren study of the dissociation of 1,1,1-trifluoroethane: An intrinsic non-RRKM process
A shock-tube, laser-schlieren study of the dissociation of 1,1,1-trifluoroethane: An intrinsic non-RRKM process
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DOI：
10.1021/jp036282h
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发表时间：
2004-04-01
影响因子：
2.9
通讯作者：
Tranter, RS
中科院分区：
文献类型：
--
作者：
Kiefer, JH;Katopodis, C;Tranter, RS
本文报道用激波管激光纹影法研究了标题三氟乙烷（CF_3CH_3-> CH_2CF_2 + HF）在1600-2400 K高温和15-550 Torr负压范围内的分子离解。密度梯度很好地拟合一个简单的两个反应机制和准确的解离速率。结果进行了比较，从G3 TS计算的k（无穷大），这是一个极好的适合现有的低T数据和可靠的外推k（无穷大）高温。推导出的速率常数显示出非常深的衰减，从这个外推，但令人惊讶的是，几乎没有变化与压力。这种特殊性是如此严重，以至于RRKM计算严重无法解释这种行为。解离似乎是一个明显的例子，一个内在的非RRKM过程（非统计解离）。这一结论得到了在解离和非解离温度下观察到的双振动弛豫的有力支持，这是慢IVR的明确证明。使用一个简单的模型，分为两组状态，深衰减被发现是一致的速率控制慢IVR，而不是低碰撞效率。该模型表明，IVR速率类似于10（8）s（-1）的解离能。
We report a shock-tube, laser-schlieren investigation of the molecular dissociation of the title trifluoroethane, CF3CH3 --> CH2CF2 + HF, over very high temperatures, 1600-2400 K, and a wide range of sub-atmospheric pressures, 15-550 Torr. The density gradients are well fit by a simple two-reaction mechanism and accurate dissociation rates obtained. The results are compared with a k(infinity) calculated from a G3 TS for this molecular elimination, which is a superb fit to the available lower-T data and a reliable extrapolation of k(infinity) to high temperatures. The derived rate constants show a very deep falloff from this extrapolation but surprisingly little variation with pressure. This peculiarity is so severe that RRKM calculations dramatically fail to account for the behavior. The dissociation seems to be a clear example of an intrinsic non-RRKM process (nonstatistical dissociation). This conclusion is strongly supported by the observation of double vibrational relaxation at both dissociating and nondissociating temperatures, an unambiguous demonstration of slow IVR. Using a simple model with division into two groups of states, the deep falloff is found to be consistent with a rate-controlling slow IVR, not with low collision efficiency. The model suggests an IVR rate of similar to10(8) s(-1) for dissociation energies.