Studies of Molecular and Cluster Fragmentation Using Synchrotron Radiation: Measurements and Models
Studies of Molecular and Cluster Fragmentation Using Synchrotron Radiation: Measurements and Models
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使用同步辐射进行分子和簇破碎的研究：测量和模型
DOI：
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发表时间：
2006
期刊：
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通讯作者：
A. Lindgren
中科院分区：
文献类型：
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作者：
A. Lindgren
一台用于研究光致碎裂的新光谱仪已经设计并投入使用。该仪器产生碎片的能量和角发射的详细视图，在小分子的情况下，可以与它们在解离时刻的几何形状相关。单，双和三离子符合的光谱轮廓进行了分析，在分子排列，和核动力学。基于分子对称性和偶极激发的模型被开发用于解释所有离子碎片测量的多符合光谱。该模型的基本原理也可以应用于高阶碎裂过程，并得到了分子动力学的图像。在分子解离的情况下，碎片的各向异性以及解离时刻分子的几何形状一直是特别感兴趣的。对氨、二氧化硫、水、臭氧和氮进行的测量显示出明确的证据，即在核心激发时由对准引起的各向异性。这提供了关于芯激发态的对称性以及几何变化的信息。各向异性间接地提供关于核心激发的局部化/离域化的信息。氧1 s到“sigma样”跃迁显示了臭氧中局部激发的明确证据，但在二氧化硫中没有。此外，该谱仪还用于氩团簇碎裂动力学效应的多符合研究。大小和能量相关的测量报告。通过研究氩2 p阈值附近的碎裂模式，发现了小（~ 5）氩团簇碎裂前核重排的证据。还提出了各种集群大小的解离的时间框架。这与描述在光谱仪中皮秒至微秒时间尺度上对解离峰形状的影响的模型有关。（减）
A new spectrometer for studying photoinduced fragmentation has been designed and commissioned. The instrument produces a detailed view of the energy and angular emission of fragments, which in the case of small molecules can be related to their geometry at the moment of dissociation. The spectral profiles for single, double and triple ion coincidences are analyzed in terms of molecular alignment, and nuclear dynamics. A model based upon molecular symmetry and dipole excitation was developed for interpreting multi-coincidence spectra where all ionic fragments are measured. The basic principles of the model can be applied to higher-order fragmentation processes as well, and a picture of molecular dynamics has been obtained. In the case of molecular dissociation, anisotropy of the fragments and thus the geometry of the molecules at the moment of dissociation has been of special interest. The measurements performed on ammonia, sulfur dioxide, water, ozone and nitrogen show clear evidence of anisotropy arising from alignment upon core excitation. This provides information on the symmetry of the core excited state as well as geometry changes. The anisotropy indirectly provides information on localization/delocalization of the core excitation. Oxygen 1s to "sigma like" transitions show clear evidence for localized excitation in ozone but not in sulfur dioxide. Moreover the spectrometer is used to perform multi-coincidence studies of dynamic effects of argon cluster fragmentation. Both size and energy dependent measurements are reported. Evidence for nuclear rearrangements before fragmentation is found for small ( ~ 5) argon clusters by studying the fragmentation patterns around the argon 2p threshold. The time frame of dissociation for various cluster sizes is also presented. This in connection with a model describing the influence on the peaks shapes for dissociation on a picosecond to microsecond time scale in the spectrometer. (Less)