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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Reaction Dynamics of Zr and Nb with Ethylene
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Reaction Dynamics of Zr and Nb with Ethylene

机译：Zr和Nb与乙烯的反应动力学

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The reactions of transition metal (M) atoms Zr and Nb with ethylene (C_2H_4) were studied using the technique of crossed molecular beams. Angular and velocity distributions of MC_2H_2 products following H_2 elimination were measured at collision energies between 5 and 23 kcal/mol using electron impact and 157 nm photoionization mass spectrometry. Photodepletion studies identify that the atomic reactants are predominantly in their ground electronic states and that the observed MC_2H_2 products result primarily from reactions of these ground-state atoms. Center-of-mass product angular distributions derived from the data indicate that reactions involve the formation of intermediate complexes having lifetimes longer than their rotational periods. Product translational energy distributions demonstrate that a large fraction of excess available energy is channeled into product internal excitation. Wide-angle nonreactive scattering of metal atom reactants following decay of long-lived MC_2H_4 association complexes was also observed for both transition metal reactants at collision energies >=9 kcal/mol, with approximately 36% of the initial translational energy converted into C_2H_4 internal excitation. At collision energies of <= 6 kcal/mol, nonreactive scattering of Zr from ZrC_2H_4 decay was found to be negligible, whereas this channel was clearly observed for Nb. RRKM modeling of the competition between decay of MC_2H_4 complexes back to M + C_2H_4 and C-H insertion forming HMC_2H_3 indicates that there exists an adiabatic potential energy barrier for M + C_2H_4 association in the case of Zr and that the transition state for this process is tighter than for the analogous process in Nb + C_2H_4. The barrier for Zr + C_2H_4 association is attributed to the repulsive s~2 ground state configuration of Zr, whereas for Nb the s~1 ground state configuration results in no barrier for association. The absence of decay of ZrC_2H_4 back to Zr + C_2H_4 at low collision energies indicates that the barrier for C-H insertion forming HZrC_2H_3 lies below the barrier for Zr + C_2H_4 association. This opens up the possibility that direct C-H insertion without initial ZrC_2H_4 formation may play an important role.
机译：采用交叉分子束技术研究了过渡金属（M）原子Zr和Nb与乙烯（C_2H_4）的反应。使用电子冲击和157 nm光电离质谱法，在5至23 kcal / mol的碰撞能量下，测定了H_2消除后MC_2H_2产物的角和速度分布。光耗尽研究表明，原子反应物主要处于基态电子状态，并且观察到的MC_2H_2产物主要来自这些基态原子的反应。从数据得出的质心产物角分布表明，反应涉及寿命长于其旋转周期的中间配合物的形成。产品转化的能量分布表明，大部分多余的可用能量被引导到产品内部激发中。还观察到两种过渡金属反应物在碰撞能量> = 9 kcal / mol时，长寿命MC_2H_4缔合配合物衰变后，金属原子反应物的广角非反应性散射，其中约36％的初始平移能转化为C_2H_4内部激发。在碰撞能量<= 6 kcal / mol时，发现Zr从ZrC_2H_4衰变的非反应性散射可以忽略不计，而该通道的Nb清晰可见。 RRKM模型对MC_2H_4配合物衰变回M + C_2H_4与形成HMC_2H_3的CH插入之间的竞争的竞争表明，在Zr的情况下，存在M + C_2H_4缔合的绝热势垒，并且该过程的过渡态比Nb + C_2H_4中的类似过程。 Zr + C_2H_4缔合的势垒归因于Zr的排斥性s〜2基态构型，而对于Nb，s〜1的基态构型没有缔合势垒。 ZrC_2H_4在低碰撞能量下没有衰减回到Zr + C_2H_4的现象表明形成HZrC_2H_3的C-H插入的势垒低于Zr + C_2H_4缔合的势垒。这开辟了直接C-H插入而没有初始ZrC_2H_4形成的可能性。

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