Steinbach Christof, Fárník Michal, Buck Udo, Brindle Carrie A, Janda Kenneth C
Max-Planck Institut für Dynamik und Selbstorganisation, Bunsenstr. 10, D-37073 Göttingen, Germany.
J Phys Chem A. 2006 Jul 27;110(29):9108-15. doi: 10.1021/jp0626061.
Clusters of krypton are generated in a supersonic expansion and size selected by deflection from a helium target beam. By measuring angular distributions for different fragment masses and time-of-flight distributions for fixed deflection angles and fragment masses, the complete fragmentation patterns for electron impact ionization at 70 eV are obtained from the dimer to the heptamer. For each of the neutral Kr(n) clusters studied, the main fragment is the monomer Kr(+) ion with a probability f(n)(1) > 90%. The probability of observing dimer Kr(2)(+) ions is much smaller than expected for each initial cluster size. The trimer ion Kr(3)(+) appears first from the neutral Kr(5), and its fraction increases with increasing neutral cluster size n, but is always much smaller than that of the monomer or dimer. For neutral Kr(7), all possible ion fragments are observed, but the monomer still represents 90% of the overall probability and fragments with n > 3 contribute less than 1% of the total. Aspects of the Kr(n) cluster ionization process and the experimental measurements are discussed to provide possible reasons for the surprisingly high probability of observing fragmentation to the Kr(+) monomer ion.
氪团簇在超声速膨胀过程中产生，并通过从氦靶束的偏转来选择尺寸。通过测量不同碎片质量的角分布以及固定偏转角和碎片质量下的飞行时间分布，可获得70 eV电子碰撞电离从二聚体到七聚体的完整碎片化模式。对于所研究的每个中性Kr(n)团簇，主要碎片是单体Kr(+)离子，其概率f(n)(1) > 90%。对于每个初始团簇尺寸，观察到二聚体Kr(2)(+)离子的概率远小于预期。三聚体离子Kr(3)(+)首先从中性Kr(5)中出现，其比例随着中性团簇尺寸n的增加而增加，但始终远小于单体或二聚体的比例。对于中性Kr(7)，观察到了所有可能的离子碎片，但单体仍占总概率的90%，且n > 3的碎片占总比例不到1%。讨论了Kr(n)团簇电离过程和实验测量的相关方面，以提供观察到碎片化形成Kr(+)单体离子的概率出奇高的可能原因。
