Structural relaxation of hydrogen bonded systems investigated by time-resolved X-ray diffraction

通过时间分辨 X 射线衍射研究氢键系统的结构弛豫

• 批准号: 5373921
• 负责人: Professor Dr. Alfred Laubereau
• 金额: --
• 依托单位: Arbeitsgruppe Laser- und Röntgenphysik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2002
• 资助国家: 德国
• 起止时间: 2001-12-31 至 2005-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5373921?language=en
• 关键词: Structural; relaxation; hydrogen; bonded; systems

Using time-resolved X-ray diffraction on an ultrashort time scale, the short-range order in molecular liquids can be monitored, providing information on structural relaxation. Of special interest for the planned investigations are the microscopic dynamics of H-bonded systems like water, aqueous electrolytic solutions, while simple alcohols may serve as model systems for comparison. It is clear that the ability of water to associate to a 3-dimensional H-bonded network results in the special features of this most important solvent. Recent experiments utilizing time-resolved infrared spectroscopy on a sub-picosecond time scale have opened the door to a more detailed picture of the hydrogen bond dynamics of water. An important disadvantage in these investigations however is that the measured spectral features have to be related to structural changes using up to now empirical rules which are debatable. A direct determination of the hydrogen bridge bond dynamics of water and related systems on the sub-picosecond time scale is lacking. A powerful method for this purpose is time-resolved small angle X-ray diffraction. The time-integrated version of the technique has demonstrated its potential in numerous cases during the past decades, providing time- and spatial averages of the short-range order in the liquid. To get access to the strutural dynamics of water a novel time-resolved version with sub-picosecond resolution has to be developed. A pump-probe approach will be utilized and built up in close collaboration with the group of W. Zinth at the Munich university. For the excitation process a femtosecond laser pulse in the UV or mid-infrared spectral range will be used initiating the breaking of hydrogen bonds in the sample. The subsequent structural changes are monitored by a sub-picosecond X-ray pulse emitted from a laser plasma generated by the help of the same high power femtosecond laser system that also delivers the pump pulse. The new experiment will provide key information on the ultrafast structural dynamics of H-bonded systems like bulk water and aqueous electrolytes relevant for biological systems. In a second stage of the project, water will be also studied under special boundary conditions, i.e. in microporous systems like zeolithes and in model systems of biological membranes.

使用时间分辨的X射线衍射在超短时间尺度上，可以监测分子液体中的短程有序，提供结构弛豫的信息。特别感兴趣的计划的调查是氢键系统，如水，电解质水溶液的微观动力学，而简单的醇可以作为模型系统进行比较。很明显，水与三维氢键网络结合的能力导致了这种最重要的溶剂的特殊性质。最近的实验利用时间分辨红外光谱在亚皮秒的时间尺度上打开了大门，以更详细的图片的氢键动力学的水。然而，在这些调查中的一个重要缺点是，测量的光谱特征必须与结构变化有关，使用到现在为止的经验规则是有争议的。在亚皮秒时间尺度上，水和相关系统的氢键键动力学的直接测定缺乏。时间分辨小角度X射线衍射是一种有效的方法。在过去的几十年中，该技术的时间积分版本已经在许多情况下证明了其潜力，提供了液体中短程有序的时间和空间平均值。为了获得水的结构动力学，必须开发具有亚皮秒分辨率的新的时间分辨版本。一个泵浦探测的方法将被利用，并建立在与W。慕尼黑大学的辛思。对于激发过程，将使用紫外或中红外光谱范围内的飞秒激光脉冲，引发样品中氢键的断裂。随后的结构变化通过从激光等离子体发射的亚皮秒X射线脉冲来监测，该激光等离子体是通过同样的高功率飞秒激光系统来产生的，该系统也提供泵浦脉冲。这项新实验将提供有关氢键系统（如与生物系统相关的散装水和含水电解质）超快结构动力学的关键信息。在该项目的第二阶段，还将在特殊的边界条件下研究水，即在沸石等微孔系统和生物膜模型系统中。