Harding Daniel, Ford Mark S, Walsh Tiffany R, Mackenzie Stuart R
Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL.
Phys Chem Chem Phys. 2007 May 7;9(17):2130-6. doi: 10.1039/b618299b. Epub 2007 Feb 16.
The reactions of gas phase rhodium clusters, Rhn+/- (n<30), with nitrous oxide, N2O, have been investigated under single collision conditions by Fourier transform ion cyclotron resonance mass spectrometry. The only significant reaction observed is the sequential generation of oxides. Absolute rate constants for the reactions of all clusters have been determined and, in the case of the cationic clusters especially, they exhibit large fluctuations as a function of cluster size with local minima observed for n=5, 19, 28. Striking similarities are observed with the variation in rate constants for these clusters in reactions with small hydrocarbons (C. Adlhart and E. Uggerud, J. Chem. Phys., 2005, 123, 214709). Corresponding size effects are also observed but are less marked in the reactions of the anionic clusters. The reactions of several clusters exhibit marked deviations from simple pseudo-first-order kinetics suggesting the presence of multiple isomeric forms: Rh11+, Rh12+ and Rh8- exhibit characteristic biexponential decays which are interpreted in terms of the existence of different structural forms of the cluster which have markedly different reactivity. By contrast, Rh6+, Rh7+ and Rh8+ show rates which apparently increase with time, probably due to collisional activation. Thermalisation of the clusters prior to reaction by exposure to pulses of argon results in changes to the kinetics of these anomalous systems which can be explained in terms of collision induced isomerisation.
通过傅里叶变换离子回旋共振质谱法，在单碰撞条件下研究了气相铑团簇Rhn+/-（n<30）与一氧化二氮（N2O）的反应。观察到的唯一显著反应是氧化物的依次生成。已确定了所有团簇反应的绝对速率常数，特别是对于阳离子团簇，它们随团簇大小呈现出很大的波动，在n = 5、19、28时出现局部最小值。在与小分子烃的反应中，这些团簇的速率常数变化呈现出惊人的相似性（C. Adlhart和E. Uggerud，《化学物理杂志》，2005年，123卷，214709页）。也观察到了相应的尺寸效应，但在阴离子团簇的反应中不太明显。几个团簇的反应明显偏离简单的准一级动力学，表明存在多种异构体形式：Rh11+、Rh12+和Rh8-呈现出特征性的双指数衰减，这可根据团簇存在具有明显不同反应活性的不同结构形式来解释。相比之下，Rh6+、Rh7+和Rh8+的反应速率明显随时间增加，这可能是由于碰撞活化。在反应前通过暴露于氩脉冲使团簇热化，会导致这些异常体系的动力学发生变化，这可以用碰撞诱导异构化来解释。
