China
Africa
Explore chapters and articles related to this topic
Theoretical X-ray Absorption Spectroscopy of Liquid Water Using First-Principles Calculations
Published in Fausto Martelli, Properties of Water from Numerical and Experimental Perspectives, 2022
In general, a X-ray absorption process could be understood as follows: within its near-edge region, a high-energy photon is absorbed and promotes a core electron to empty states, which should be allowed under the selection rules. X-ray Raman scattering (XRS) is a technique which can provide similar information to X-ray absorption spectroscopy (XAS). The core processes occur at a time scale of femtoseconds that is much faster than any molecular vibrational movements, that is, the vibration of HB network of water. As such, XAS could capture the instantaneous snapshots of the structure of liquid water during the X-ray measurement. Moreover, it is found that the pre-edge feature of the XAS spectra for liquid water comes from the bound exciton while the main edge and post-edge features originate from the contributions of the resonant excited states, the first one is more sensitive to the local structure compared to the latter two. Therefore, XAS spectroscopy could be good for probing the local structure of liquid water.
Construction of a spherically bent crystal analyzer through anodic bonding for a non-resonant inelastic X-ray scattering spectrometer
Published in Instrumentation Science & Technology, 2021
In a non-resonant IXS (NRIXS or X-ray Raman Scattering; XRS) spectroscopy, which is a hard X-ray alternative to X-ray absorption spectroscopy (XAS) for measuring the soft X-ray absorption edges, inelastically scattered X-rays from the sample are energy analyzed by spherically bent multi-crystal analyzers and focused on the area detector. Several groups of spherically bent analyzers are placed at different locations on the Rowland circle so that the required momentum transfer range can be covered.[6] Since the energy resolution, background, momentum transfer, and efficiency of each analyzer within an analyzer set may vary, data evaluation must be done individually for each analyzer. For this purpose two-dimensional pixel detectors are utilized, which allow to record the focus of each analyzer on a different spot of the detector area.[7] Point-to-point focusing of bent crystal analyzers on two-dimensional pixel detector enables X-ray imaging of the sample and its environment.[8] This feature is highly advantageous for visualization and alignment purposes in complicated sample setups such as in-situ conditions. X-ray imaging capability of XRS also provides to perform single-shot direct tomography. An area detector with a pixel size of 55 × 55 μm2 or less is required to make X-ray imaging possible in XRS experiments.[9]