利用超瑞利散射，我們能夠得知有機分子的超極化率，從而幫助我們對其在液態時的結構及相互作用加深認識和了解。在此研究項目，我們將通過測量對-硝基苯胺溶劑或硝基苯之稀釋混合物的超瑞利散射退極化比，分別提取當中的相干以及非相干散射訊號，並對分子間互相的位置以及方向相關性進行研究。同時，我們將針對分子間的短程和長程相互作用，利用其分別衍生的局域相干散射與離域相干散射進行深入探討。研究顯示，退極化比會受分子間的平均距離所影響，而實驗中將利用對-硝基苯胺在溶液中的濃度或硝基苯的稀釋率對平均距離進行調整。粗略估算當分子間的相互作用能與熱能的強度可比時，退極化比將會有明顯的變化。研究中我們運用簡單的偶極硬球模型，假設分子間為經典的電偶極子相互勢能，同時只考慮一對分子之間的直接相互作用，並以球直徑作為唯一參數擬合實驗結果。另一方面，通過觀察實驗中違反局域散射的對稱性，我們證實硝基苯分子間存在著長程相關性。而以不同溶劑進行稀釋，例如甲醇和丙酮時，會破壞其長程相關性，但當其與苯類溶劑，如對-二甲苯混合時，則會保持其長程相關性。因此，分子之間的長程相關性曾被認為是來自苯環之間的π-π相互作用。過往曾經有研究提出一項將液體中的集體震動模式以震動子(libron)表示的模型，能夠解釋觀察到的不對稱性，但此模型的擬合結果與此實驗中硝基苯以甲醇稀釋，並將其相關性破壞的結果並不相符。另外，以苯甲醇稀釋的結果與純硝基苯之間的不對稱現象相反，令π-π相互作用的假設受到質疑。直至現在，仍未有一項合理的模型能解釋得到實驗中所觀察到分子間的長程相關性。 / Hyper-Rayleigh Scattering (HRS) can be used to determine the first hy-perpolarizability β and examine the structure of organic compounds in liquid states. In this research project, by studying the HRS depolarization ratios of solutions of para-nitroaniline (PNA) or diluted mixtures of nitrobenzene, coherent and incoherent scattering signals were extracted for investigation of the spatial and angular correlations between molecules in a liquid state. Both the localized coherent light scattering, which is controlled by the strength of short-range intermolecular interaction, and the delocalized coherent scattering, which is related to the long range correlation between molecules, were revealed. The depolarization ratios were found to depend on the intermolecular distance, which varied with the concentration of the PNA in the solution or the dilution ratio of pure nitrobenzene in various solvents. A rough estimation shows that significant depolarization ratio variation should occur when the interactionenergy becomes comparable to the thermal energy. With the pair correlations calculated by a dipolar hard sphere model that assumed a classical dipolar interaction potential, the experimental results can be accounted by the theory using the hard sphere diameter as the only fitting parameter. The long range correlation between molecules was confirmed to exist even in the liquid state of pure nitrobenzene by observing a deviation from the local scattering symmetries. The long range correlation between nitrobenzene molecules was found to be easily destroyed by mixing with various solvents such as methanol and acetone, but was maintained by mixing with p-xylene, which is a solvent with benzene-like molecules. The π-π inter-action between the molecules was proposed to be the origin of the long range correlations. A model of delocalized collective mode (libron) that coexists with localized orientational diffusion mode in the solution was previously introduced to explain the observed phenomena. However, break downof the long range correlation by dilution using methanol showed a disagreement with the fitting of the libron model. Furthermore, use of benzol alcohol as a dilutant gives an opposite effect on the long range correlations of the nitrobenzene molecules, which makes the π-π interaction model for long range correlation between nitrobenzene molecules questionable. Presently, there is no satisfactory model on the long range correlation between molecules that can explain all our experimental results. / Detailed summary in vernacular field only. / Chan, Yan Chun = 有機溶液之相干超瑞利散射研究 / 陳恩進. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 129-132). / Abstracts also in Chinese. / Chan, Yan Chun = You ji rong ye zhi xiang gan chao rui li san she yan jiu / Chen Enjin. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgement --- p.v / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Basic Theory --- p.7 / Chapter 2.1 --- Introduction to nonlinear optics --- p.7 / Chapter 2.2 --- Harmonic generation --- p.10 / Chapter 2.3 --- Nonlinear optical phenomena --- p.12 / Chapter 2.4 --- Frequency dependent susceptibility --- p.13 / Chapter 2.5 --- Classical model to susceptibility --- p.14 / Chapter 2.6 --- Calculation of the Nonlinear Processes using Schrödinger Equation --- p.18 / Chapter 2.7 --- Densitymatrix formulation. --- p.20 / Chapter 2.8 --- Hyper-Rayleigh Scattering (HRS) --- p.23 / Chapter 3 --- Experimental Setup and Procedures --- p.30 / Chapter 3.1 --- Experimental Setup --- p.30 / Chapter 3.2 --- Instruments --- p.32 / Chapter 3.2.1 --- Laser System --- p.32 / Chapter 3.2.2 --- Sample cells --- p.33 / Chapter 3.2.3 --- Camera Lens --- p.34 / Chapter 3.2.4 --- Numerical Aperture --- p.35 / Chapter 3.2.5 --- Monochromator --- p.35 / Chapter 3.2.6 --- Photomultiplier --- p.35 / Chapter 3.2.7 --- Photon counter --- p.36 / Chapter 3.3 --- Experimental procedures --- p.37 / Chapter 3.3.1 --- Sample preparation --- p.37 / Chapter 3.3.2 --- Focus point calibration --- p.37 / Chapter 3.3.3 --- Measurement of depolarized intensities and ratios --- p.41 / Chapter 4 --- Instrumental calibration and error analysis --- p.43 / Chapter 4.1 --- PMT applied voltage and photon counter discrimination level --- p.43 / Chapter 4.2 --- HRS wavelength and spectral width --- p.46 / Chapter 4.3 --- Polarizations --- p.50 / Chapter 4.4 --- Slit width --- p.52 / Chapter 4.5 --- Pulsed laser repetition rate --- p.53 / Chapter 4.6 --- Gate width and gate delay --- p.55 / Chapter 4.7 --- Statistical error --- p.57 / Chapter 4.8 --- Photon counting error --- p.61 / Chapter 4.9 --- Numerical aperture collimation --- p.63 / Chapter 4.10 --- Depolarization ratio bias --- p.65 / Chapter 4.11 --- Laser focusing point deviation --- p.69 / Chapter 5 --- Measurement and results of localized coherent Hyper-Rayleigh scatterings --- p.74 / Chapter 5.1 --- Modeling of localized coherent scattering --- p.76 / Chapter 5.2 --- Localized coherent scattering of PNA --- p.84 / Chapter 5.3 --- Localized coherent scattering of Nitrobenzene --- p.91 / Chapter 5.4 --- Study with absorption spectrum --- p.96 / Chapter 5.5 --- Non-zero hyperpolarizability off-diagonal elements --- p.101 / Chapter 6 --- Study of delocalized coherent Hyper-Rayleigh scattering --- p.105 / Chapter 6.1 --- Delocalized coherent scattering of PNA --- p.106 / Chapter 6.2 --- Delocalized coherent scattering of nitrobenzene --- p.110 / Chapter 6.3 --- Libronmodel --- p.115 / Chapter 6.4 --- Long range correlations of PNAmolecules --- p.118 / Chapter 6.5 --- Ionic contaminations --- p.120 / Chapter 6.6 --- Long range correlations of other liquids --- p.123 / Chapter 7 --- Conclusions --- p.125 / Bibliography --- p.129
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328585 |
| Date | January 2012 |
| Contributors | Chan, Yan Chun., Chinese University of Hong Kong Graduate School. Division of Physics. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xviii, 132 leaves) : ill. (some col.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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