High density collection of molecular ion clusters and their photoexcitation dynamics

分子离子簇的高密度收集及其光激发动力学

基本信息

批准号：
07454190
负责人：
NISHI Nobuyuki
金额：
$ 4.99万
依托单位：
Okazaki National Research Institutes (1996-1997)Kyushu University (1995)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

In order to study electronic states and dynamics of highly condensed molecular ion clusters, we designed a molecular beam apparatus with a soft-landing ion deosition and IR and UVabsorption spectrometers. A molecular beam generated from liquid droplets by adiabatic Big-Bang explosion is directly injected against 10-inch diffusion pump. Ions are extracted perpendicular to the beam axis, mass-selected, decelerated, and gently imbedded in a rare gas matrix. As atest experiment, benzene cations are deposited in argon matrices at 4 K.Contamination of the background neutral benzene was so little that after 10 hour deposition we can detect the neutrals by UV absorption spectrometry. The electronic spectrum of benzene cation showed that the electronic orbitals of argon atoms around the cation is highly distorted and polarized by the cation. The high dnsity deposition process was accompanied with a big difficulty without any codeposition of negative ions. Frequent explosive ablation of the new surface layrs was observed during the deposition. It is necessary to design a natural negative ion deposition mechanism in a chamber.We also observed a charge hopping phenomenon in benzene trimer cations after vibrational excitation of a C-H stretching motion of an ionic molecule. The excitation of an isotopic mixture (C_6H_6) ^+ (C_6D_6)_2 resulted in the fragmentation yielding (C_6D_6)_2^+ and [ (C_6D_6) (C_6H_6) ]^+ with a ratio of 1 : 2. This is a statistical limit suggesting the hopping occurs sufficiently faster than the dissociation process. The observed line-widths of the C-H stretching bands showed sectral shifts dependent on the position of the charged molecules in the cluster and also on the masses of the neighboring molecules. Rather broad line-widths indicates that the relaxation is of the order of 100-150fs.

为了研究高度凝聚的分子离子簇的电子态和动力学，我们设计了具有软着陆离子沉积以及红外和紫外吸收光谱仪的分子束装置。由绝热大爆炸产生的液滴产生的分子束直接注入10英寸扩散泵。垂直于束轴提取离子、进行质量选择、减速并轻轻地嵌入稀有气体基质中。作为测试实验，苯阳离子在 4 K 下沉积在氩基质中。背景中性苯的污染非常少，沉积 10 小时后我们可以通过紫外吸收光谱法检测到中性物质。苯阳离子的电子谱表明，阳离子周围的氩原子的电子轨道被阳离子高度扭曲和极化。在没有任何负离子共沉积的情况下，高密度沉积过程伴随着很大的困难。在沉积过程中观察到新表面层频繁发生爆炸性烧蚀。有必要在腔室中设计自然的负离子沉积机制。我们还观察到离子分子的C-H伸缩运动振动激发后苯三聚体阳离子中的电荷跳跃现象。同位素混合物 (C_6H_6) ^+ (C_6D_6)_2 的激发导致碎片产生 (C_6D_6)_2^+ 和 [ (C_6D_6) (C_6H_6) ]^+，比率为 1 : 2。这是统计极限表明跳跃发生得比解离过程快得多。观察到的 C-H 伸缩带的线宽显示出扇区位移，具体取决于簇中带电分子的位置以及相邻分子的质量。相当宽的线宽表明弛豫约为 100-150fs。