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Infrared and Raman spectroscopy of molecules and molecular aggregates in helium droplets.

机译：氦液滴中分子和分子聚集体的红外和拉曼光谱。

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摘要

This dissertation covers several different aspects of spectroscopy of molecules and molecular clusters embedded in low-temperature matrices, such as helium droplets. First, details on the formation and optimization of He droplets will be discussed. A new method of measuring droplet sizes for cw nozzle expansions using mass spectrometry was developed. The results of the measurements of the sizes of the droplets in pulsed expansion as a function of temperature will be described. Details on the electron-impact ionization of He droplets will also be discussed as well as a simple method of modeling the ionization and excitation of He atoms in the droplet. In addition, preliminary measurements on the size distribution of He droplets produced at very low temperature of 5--7 K in continuous expansion will be addressed.;Using matrix isolation in He droplets, vibrational spectra of clusters consisting of para-H2 or para-H2/D2 have been obtained using coherent anti-Stokes Raman spectroscopy (CARS). The vibrational frequency of para-H2 molecules obtained upon expansion of neat para-H2/D2 gas or liquid was found to be very similar to that in bulk solid samples having equal composition. On the other hand, spectra in clusters obtained upon expansion of 1% para-H2/D 2 clusters seeded in He are liquid and have a considerable frequency shift, which indicate phase separation of the two isotopes in clusters at low temperature. The onset of phase separation in para-H2/D 2 mixtures is predicted at approximately 3 K providing further evidence of super-cooled liquid hydrogen clusters.;To address the Raman spectra observed in liquid H2 clusters, vibrational and rotational spectra of bulk liquid para-H2 at temperature of T = 14 -- 26 K and of solid at T = 6 -- 13 K have been obtained using coherent anti-Stokes Raman scattering technique. The vibrational frequency in the liquid increases with temperature by about 2 cm-1, and the shift scales with the square of the sample's density. An extrapolation of the vibrational frequency in the metastable para-H2 liquid below the freezing point is discussed. The results indicate that the vibron hopping between the molecules is active in the liquid, similar to that previously found in the solid.;Matrix isolation has also been performed in argon solid matrices based on a custom-made cryogenic optical cell. Single water molecules have been isolated in solid Ar matrices at 4 K and studied by ro-vibrational spectroscopy using FTIR in the regions of the nu1, nu2, and nu 3 modes. Upon nuclear spin conversion at 4 K, essentially pure para-H2O was prepared followed by subsequent fast annealing generating ice particles. FTIR studies of the vapor above the condensed water upon annealing to T ≥ 250 K indicate fast re-conversion of nuclear spin to equilibrium conditions. Our results indicate that nuclear spin conversion is fast in water dimers and larger clusters, which preclude preparation of concentrated samples of para-H2O, such as in ice or vapor.
机译：本文涵盖了低温基质中嵌入的分子和分子簇的光谱学的几个不同方面，例如低温氦滴。首先，将讨论有关He液滴的形成和优化的细节。开发了一种使用质谱法测量连续喷嘴喷嘴液滴尺寸的新方法。将描述脉冲膨胀中液滴尺寸随温度变化的测量结果。还将讨论有关He液滴的电子撞击电离的细节，以及对液滴中He原子的电离和激发进行建模的简单方法。另外，将对在5--7 K的极低温下连续膨胀产生的He液滴的尺寸分布进行初步测量。;利用He液滴中的基质隔离作用，由对H2或对H组成的簇的振动光谱使用相干抗斯托克斯拉曼光谱仪（CARS）获得了H2 / D2。发现在纯对-H2 / D2气体或液体膨胀后获得的对-H2分子的振动频率与具有相同组成的散装固体样品中的振动频率非常相似。另一方面，在He中播种1％对-H2 / D 2簇时获得的簇中的光谱是液体，并且具有相当大的频移，这表明低温下簇中两个同位素的相分离。对-H2 / D 2混合物的相分离预计在大约3 K处发生，这提供了过冷液态氢簇的进一步证据。使用相干抗斯托克斯拉曼散射技术获得了T = 14-26 K温度下的-H2和T = 6-13 K下的固体。液体中的振动频率随温度增加约2 cm-1，并且位移与样品密度的平方成比例。讨论了在低于冰点的亚稳态对H2液体中振动频率的外推法。结果表明分子之间的振子跳跃在液体中是活跃的，类似于先前在固体中发现的。；也已经在基于定制的低温光学电池的氩气固体基质中进行了基质分离。已在4 K的固态Ar矩阵中分离出单个水分子，并使用FTIR在nu1，nu2和nu 3模式区域通过旋转振动光谱法进行了研究。在4 K下进行核自旋转化后，制备了基本纯的对H2O，随后进行快速退火以生成冰粒。退火至T≥250 K时，冷凝水上方的蒸气的FTIR研究表明，核自旋迅速重新转化为平衡状态。我们的结果表明，核自旋转化在水二聚体和较大的团簇中快速进行，这排除了制备对-H2O浓缩样品的能力，例如在冰或蒸汽中。

著录项

  • 作者

    Sliter, Russell Thomas.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Chemistry Analytical.;Chemistry Inorganic.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 238 p.
  • 总页数 238
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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