Experimental study of the reaction of molecules whose vibrational distribution is perturbed.

在化学动力学领域，研究局部振动激发分子与一般分子的不同行为是非常重要的。从理论上讲，这是基于IRC与其他振动模式之间的耦合进行讨论的。另一方面，由于观察难度大，实验研究报道较少。在本课题中，我们尝试将激波加热方法与CO_2红外激光射击相结合，观察反应行为。用该方法研究了激光照射后丙烯腈在激波加热区发生分解的过程。由于激光功率小于10mJ，激光照射仅对振动态的热分布产生扰动。另一种产生局部振动激发分子的方法是对较大的分子进行热分解。如果乙基乙烯醚被单分子分解，则产生乙醛和乙烯。该反应的过渡态具有6中心结构，该结构表明产物醛的甲基以旋转或H-C-H弯曲模式被强烈激发。因此，预计在这种情况下产生的乙醛会表现出不寻常的动力学。事实上，我们发现这种醛的分解速率常数比通常的值大得多。因此，我们确定了振动的局部激励敏感地影响单分子分解速率。

It is very important in the field of chemical kinetics to investigate that local-vibration-excited molecules behave different mannor from the usual molecules. Theortically, this is discussed on the basis of the coupling of the vibrational modes between the IRC and others. On the other hand, there are few report on the experimental study because of the difficulty of the obserbation. In this project, we tried to observe the reaction behavior by connecting the shock heating method and CO_2 infra-red laser shot. With this method it was found that acrylonitrile was decomposed after laser shot in the shock heated region. Since the laser power was less than 10mJ, laser shot merely perturbed the thermal disrtribution of the vibrational states.The other method to produce local-vibration-excited molecules was the thermal decompositon of relatively large molecules. If ethyl vinyl ether is decomposed unimolecularly, acetaldehyde and ethylene are produced. The transition state of this reaction have a 6-centered structure and this structure suggests that the methyl group of the product aldehyde is strongly excited in the rotation or H-C-H bending mode. Therefore, it is expected that the acetaldehyde produced in this monnor behaves unusual kinetics. In fact, we found that this aldehyde decomposed with very large rate constants compared with the usual value.Thus, we ascertained that the local excitation of vibrations affected sensitively the unimolecular decomposition rate.