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Study of formation and stability of helium cluster ions with a very low temperature drift tube

极低温漂移管氦簇离子的形成及稳定性研究

基本信息

批准号：
01460047
负责人：
KOBAYASHI Nobuo
金额：
$ 4.16万
依托单位：
Tokyo Metropolitan University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1991
项目状态：
已结题

项目摘要

A drift tube whose length is 10 cm is settled in a cryogenic system and cooled by liquid helium. In normal condition, the temperature of helium gas in the tube is about 4.5 k. When the liquid helium reservoir is evacuated with a pumping system, the temperature is lowered down to 3.5 k. Ions mass selected are injected into the tube. These ions are quickly thermalized by elastic collisions with He atoms and drift toward the end of the tube by a uniform electric field. Clusters are formed through three body collisions with He atoms during drifts of ions. The ions exited from the end of the tube are mass analyzed with a quadruple mass filter. Effective temperatures of the drifting ions are controlled by changing the electric field strength in the tube. Using this technique, following experiments have been made.1). Stability of RgHe^+_ (Rg=He, Ne, Ar and Kr) have been studied. When the effective temperature of the ions are rather high, the clusters with larger size are dissociated by collisions with He atoms. Therefore, by measuring size distributions of clusters at various electric field strength, we can obtain an information on the stability of the clusters. It is suggested that an icosahedral structure with core ions He_2^+, NeHe^+, Ar^+ and Kr^+ is stable for RgHe_n^+ (Rg=He, Ne, Ar and Kr), respectively.2) Stability of H^+He_n and H_3^+He_n. In the case of H^+He_n clusters, it is suggested that the stable structure is the icosahedron with the core ion HHe^+ like rare gas ions. On the other hand, for H_3^+He_n quite different structure with the magic number of n=10 and 11 is suggested to be stable.3) Ion mobilities of He^+, Ne^+, Ar^+ and Kr^+ have been measured at gas temperature of 4.4 k. Many interesting features have been observed. Especially in the case of He^+, it has been found that the reduced mobility decreases below E/N=5 Td which may be attributed to an orbitting resonance.

将长度为10 cm的漂移管放置在低温系统中并通过液氦冷却。正常情况下，管内氦气温度约为4.5K当用泵系统抽空液氦容器时，温度降低到3.5K。将选择的离子质量注入管中。这些离子通过与He原子的弹性碰撞迅速热化，并通过均匀电场向管的末端漂移。团簇是在离子漂移过程中与He原子发生三体碰撞而形成的。从管的端部退出的离子用四重质量过滤器进行质量分析。漂移离子的有效温度是通过改变管中的电场强度来控制的。利用该技术进行了以下实验。本文研究了RgHe^+_（Rg=He，Ne，Ar和Kr）的稳定性。当离子的有效温度较高时，较大尺寸的团簇与He原子碰撞解离。因此，通过测量团簇在不同电场强度下的尺寸分布，我们可以获得团簇稳定性的信息。结果表明，对于RgHe_n^+（Rg=He，Ne，Ar和Kr），以He_2^+，NeHe^+，Ar^+和Kr^+为核心离子的二十面体结构是稳定的。对于H^+He_n团簇，其稳定结构是以HHe^+为核心离子的二十面体。3）在4.4K气体温度下，测量了He^+、Ne^+、Ar^+和Kr^+的离子迁移率。观察到许多有趣的特征。特别是在He^+的情况下，已经发现约化迁移率在E/N=5 Td以下降低，这可能归因于轨道共振。