J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague, Czech Republic.
J Chem Phys. 2011 Sep 14;135(10):104305. doi: 10.1063/1.3633474.
Pickup of several molecules, H(2)O, HBr, and CH(3)OH, and Ar atoms on free Ar(N) clusters has been investigated in a molecular beam experiment. The pickup cross sections of the clusters with known mean sizes, Ñ≈ 150 and 260 were measured by two independent methods: (i) the cluster beam velocity decrease due to the momentum transfer of the picked up molecules to the clusters, and (ii) Poisson distribution of a selected cluster fragment ion as a function of the pickup pressure. In addition, the pickup cross sections were calculated using molecular dynamics and Monte Carlo simulations. The simulations support the results of the velocity measurements. On the other hand, the Poisson distributions yield significantly smaller cross sections, inconsistent with the known Ar(N) cluster sizes. These results are discussed in terms of: (i) an incomplete coagulation of guest molecules on the argon clusters when two or more molecules are picked up; and (ii) the fragmentation pattern of the embedded molecules and their clusters upon ionization on the Ar cluster. We conclude that the Poisson distribution method has to be cautiously examined, if conclusions should be drawn about the cluster cross section, or the mean cluster size Ñ, and the number of picked up molecules.
在分子束实验中研究了自由 Ar(N) 团簇对几种分子（H(2)O、HBr 和 CH(3)OH 以及 Ar 原子）的吸附。通过两种独立的方法测量了具有已知平均大小Ñ≈150 和 260 的团簇的吸附截面：(i) 由于被吸附分子向团簇传递动量，团簇束速度降低，以及 (ii) 作为吸附压力函数的选定团簇片段离子的泊松分布。此外，还使用分子动力学和蒙特卡罗模拟计算了吸附截面。模拟结果支持速度测量的结果。另一方面，泊松分布产生的截面要小得多，与已知的 Ar(N) 团簇大小不一致。这些结果从以下几个方面进行了讨论：(i) 当吸附两个或更多分子时，客体分子在氩团簇上不完全凝聚；以及 (ii) 嵌入分子及其在 Ar 团簇上电离时的碎裂模式。我们得出结论，如果要得出关于团簇截面或平均团簇大小Ñ和吸附分子数量的结论，则必须谨慎检查泊松分布方法。
