It is also preferred for experimental reasons as X-rays at higher energies are attenuated less by the air path, the buffer solution in which the sample is made, and the cryostat windows. Range-extended XAS In general, EXAFS spectra of systems which Selleck eFT-508 contain adjacent elements in the periodic table have a limited EXAFS range due to the presence of the rising edge of the next element, thus limiting

the EXAFS distance resolution. For the Mn K-edge EXAFS studies of PS II, the absorption edge of Fe in PS II limits the EXAFS energy range (Fig. 4). Traditional EXAFS spectra of PS II samples are collected as an excitation spectrum by electronically windowing the Kα fluorescence (2p to 1s, at 5,899 eV) from the Mn atom. The solid-state detectors that have been used over the past decade have a resolution of about 150–200 eV (FWHM) at the Mn K-edge, making

it impossible to discriminate Mn fluorescence from that of Fe Kα fluorescence (at 6,404 eV). The presence of the obligatory 2–3Fe/PS II (Fe edge at 7,120 eV) limits, the data to a k-range of ~11.5 Å−1 (k = 0.51 ΔE1/2, the Mn edge is at 6,540 eV and ΔE = 580 eV). The Mn–Mn and Mn–ligand distances that can be resolved in a typical EXAFS experiment are given by $$ \Updelta R = \pi / 2k_ \max , $$ (11)where k max is the maximum energy of the photoelectron of Mn. Fig. 4 a Left (top): X-ray fluorescence of Mn and Fe. The multi-crystal monochromator with 1 eV resolution is tuned to the Mn Kα1 peak (red spectrum). Left (below): fluorescence peaks of Mn and Fe as detected using Ge-detector. The fluorescence peaks are convoluted with the electronic

selleck kinase inhibitor window resolution of 150–200 eV of the Ge-detector (black and green spectra for Mn and Fe fluorescence). Note different energy scales for the schemes shown above and below. Iron is an obligatory element in functional PS II complexes. Right: Comparison of the traditional check details Mn K-edge EXAFS spectrum (blue) from the S1 state PS II sample obtained with a traditional 30-element energy-discriminating Ge-detector with a spectrum collected using the high-resolution crystal monochromator (note the absence of Fe contribution). The dashed line at k = 11.5 Å−1 denotes the spectral limit of a conventional EXAFS experiment owing to the iron edge. Use of the high-resolution detector eliminates the Selleck MK-4827 interference of Fe and removes the limit of the energy range for Mn EXAFS data collection. b The comparison of the k-space Mn EXAFS collected with a crystal monochromator and a Ge-detector. The range of data, as indicated by k max, is inversely proportional to the resolution of the data The use of a high-resolution crystal monochromator (see the article by Bergmann and Glatzel, this issue) allows us to selectively separate the Mn K fluorescence from that of Fe (Fig. 4), resulting in the collection of data to higher photoelectron energies and leading to increased distance resolution of 0.1 Å.