作者: Morbid 時(shí)間: 2025-3-21 23:24 作者: Indolent 時(shí)間: 2025-3-22 03:47
Textbook 20001st editionce by the lattice to a vast number of observable "reflections" with characteristic directions in space is called X-ray diffraction. The method by which the directions and the intensities of these reflections are measured, and the ordering of the atoms in the crystal deduced from them, is called X -r作者: TAP 時(shí)間: 2025-3-22 05:05
Errors and Pitfalls, structure model largely reflects reality, and gives a credible .-factor although some small, but possibly important, parts of the structure are wrong. These can arise, for example, when the refinement converges not to the . but to a local . In such a case, a solution has been obtained which contain作者: 損壞 時(shí)間: 2025-3-22 12:05 作者: 完成 時(shí)間: 2025-3-22 15:51
Springer-Verlag Berlin Heidelberg 2000作者: 完成 時(shí)間: 2025-3-22 20:48 作者: 委派 時(shí)間: 2025-3-23 00:53 作者: Ingratiate 時(shí)間: 2025-3-23 04:56 作者: cardiac-arrest 時(shí)間: 2025-3-23 06:23 作者: 水槽 時(shí)間: 2025-3-23 11:08 作者: 評(píng)論性 時(shí)間: 2025-3-23 17:27
Third Parties and Exploitation,o how the various intensities associated with the reflections . arise. It will then become clear how the measurement of the intensities of a large number of reflections can reveal the arrangement of atoms in the unit cell.作者: grieve 時(shí)間: 2025-3-23 19:36
Conclusion: The Legacies of Wolfenden,here is a mirror plane in the unit cell of a structure implies that the positions of only half the atoms need be determined in order to fully describe the structure. Knowledge that there is an inversion center in the diffraction pattern makes it necessary to measure only half of the available reflec作者: arsenal 時(shí)間: 2025-3-23 23:20
it which describes the crystal structure reasonably well. There are, however, still substantial errors in these parameters, which arise partly from the approximations of the method of solution, partly from errors in evaluating the maxima in the Fourier synthesis, and partly, of course, from errors i作者: 敵手 時(shí)間: 2025-3-24 05:28
cattering atoms alter the radiation neither in amplitude nor in phase (except for the phase shift of π implicit in the scattering of electromagnetic waves). The calculation has been based on atomic scattering factors .. whose vectorial addition takes into consideration the displacements of the atoms作者: Bone-Scan 時(shí)間: 2025-3-24 09:11 作者: Arb853 時(shí)間: 2025-3-24 11:28 作者: xanthelasma 時(shí)間: 2025-3-24 15:27 作者: 食道 時(shí)間: 2025-3-24 22:56 作者: 被告 時(shí)間: 2025-3-24 23:14
The results of crystal structure determinations form the basis of several large databases, which are accessible in most countries of the world through local organisations. Three of these contain most of the data of interest to chemical crys-tallographers. They may be accessed at national centers, and they are available on CD-ROM.作者: 加入 時(shí)間: 2025-3-25 06:05
The following summary gives an overview of the steps in an X-ray structure deter-mination, together with the chapters and sections in which a more detailed account may be found.作者: nascent 時(shí)間: 2025-3-25 09:01
In this chapter, the most important stages in a structure determination will be given using as an example the thiourea adduct of N-salicylideneglycinatocopper(II) Cu(sg)SC(NH.)., (“CUHABS,” molecular formula C.H.N.O.SCu, C. Friebel, Marburg: cf. Fig. 12.5–12.7). Computer output is given in an abbreviated form and commentated in italic.作者: myopia 時(shí)間: 2025-3-25 13:10
Experimental Methods,This chapter deals with the most important methods for obtaining the necessary data for an X-ray single crystal structure determination. The first step, naturally, is the obtaining of a suitable crystal.作者: 含水層 時(shí)間: 2025-3-25 15:50
Structure Solution,The direct results of the experimental measurements for a crystal structure are: the unit cell parameters, the space group (or at least a small selection of possibilities) and the intensity data. The real purpose of the work, however, remains — the location of the atoms in the unit cell.作者: 令人作嘔 時(shí)間: 2025-3-25 20:35
Interpretation and Presentation of Results,Despite all the possible pitfalls and errors described in the last chapter, crystal structures usually arrive at the point where the refined model is ready to be converted into structural parameters of interest to chemists.作者: GORGE 時(shí)間: 2025-3-26 00:41
Crystallographic Databases,The results of crystal structure determinations form the basis of several large databases, which are accessible in most countries of the world through local organisations. Three of these contain most of the data of interest to chemical crys-tallographers. They may be accessed at national centers, and they are available on CD-ROM.作者: 徹底檢查 時(shí)間: 2025-3-26 04:33 作者: circumvent 時(shí)間: 2025-3-26 12:18
Worked Example of a Structure Determination,In this chapter, the most important stages in a structure determination will be given using as an example the thiourea adduct of N-salicylideneglycinatocopper(II) Cu(sg)SC(NH.)., (“CUHABS,” molecular formula C.H.N.O.SCu, C. Friebel, Marburg: cf. Fig. 12.5–12.7). Computer output is given in an abbreviated form and commentated in italic.作者: BRAWL 時(shí)間: 2025-3-26 16:12 作者: 駕駛 時(shí)間: 2025-3-26 19:45
Third Parties and Exploitation,o how the various intensities associated with the reflections . arise. It will then become clear how the measurement of the intensities of a large number of reflections can reveal the arrangement of atoms in the unit cell.作者: conscribe 時(shí)間: 2025-3-26 22:59 作者: Ige326 時(shí)間: 2025-3-27 02:46 作者: periodontitis 時(shí)間: 2025-3-27 07:34 作者: ITCH 時(shí)間: 2025-3-27 13:22
Structure Refinement,it which describes the crystal structure reasonably well. There are, however, still substantial errors in these parameters, which arise partly from the approximations of the method of solution, partly from errors in evaluating the maxima in the Fourier synthesis, and partly, of course, from errors in the measured data.作者: 到婚嫁年齡 時(shí)間: 2025-3-27 15:43
The Reciprocal Lattice,ture determination, it is necessary to determine the precise orientations of the crystal relative to the X-ray beam required to bring each set of lattice planes in turn into the position that fulfils the Bragg condition and causes the scattered radiation to fall on the detector system.作者: AGONY 時(shí)間: 2025-3-27 20:28
Broadway on Film: , (Beaumont 1923),sts of several such units, which may be converted into one another by symmetry operations (as in Fig. 2.2). The three vectors ., ., ., which describe the translations of the motif in space are called the basis vectors.作者: Intend 時(shí)間: 2025-3-27 23:14 作者: Mets552 時(shí)間: 2025-3-28 04:39 作者: 柔聲地說 時(shí)間: 2025-3-28 09:05 作者: Spongy-Bone 時(shí)間: 2025-3-28 12:24
Crystal Lattices,sts of several such units, which may be converted into one another by symmetry operations (as in Fig. 2.2). The three vectors ., ., ., which describe the translations of the motif in space are called the basis vectors.作者: faction 時(shí)間: 2025-3-28 15:01 作者: lipids 時(shí)間: 2025-3-28 19:27 作者: 廢止 時(shí)間: 2025-3-29 01:32 作者: PANG 時(shí)間: 2025-3-29 04:41
Third Parties and Exploitation,ture determination, it is necessary to determine the precise orientations of the crystal relative to the X-ray beam required to bring each set of lattice planes in turn into the position that fulfils the Bragg condition and causes the scattered radiation to fall on the detector system.作者: 小卒 時(shí)間: 2025-3-29 08:31
Crystal Lattices,of a crystal, it is thus only necessary to know the simplest repeating “motif” and the lengths and directions of the three vectors which together describe its repetition in space (Fig. 2.1). The motif can be a molecule, as in Fig. 2.1, or the building block of a network structure. Normally, it consi作者: 圣歌 時(shí)間: 2025-3-29 15:14
The Geometry of X-Ray Diffraction, expected when radiation with a wavelength of the order of the lattice spacings interacts with the crystal. In the following sections, the production of the necessary monochromatic X-rays will be described.作者: anus928 時(shí)間: 2025-3-29 15:35 作者: 閑蕩 時(shí)間: 2025-3-29 22:24 作者: Onerous 時(shí)間: 2025-3-30 02:09 作者: IDEAS 時(shí)間: 2025-3-30 05:07
Structure Refinement,it which describes the crystal structure reasonably well. There are, however, still substantial errors in these parameters, which arise partly from the approximations of the method of solution, partly from errors in evaluating the maxima in the Fourier synthesis, and partly, of course, from errors i作者: PACT 時(shí)間: 2025-3-30 11:55
Additional Topics,cattering atoms alter the radiation neither in amplitude nor in phase (except for the phase shift of π implicit in the scattering of electromagnetic waves). The calculation has been based on atomic scattering factors .. whose vectorial addition takes into consideration the displacements of the atoms作者: Aids209 時(shí)間: 2025-3-30 13:53
Errors and Pitfalls,l of accuracy which can only very exceptionally be obtained by spectroscopic methods. The indirect nature of the structure determination, depending as it does on the acceptance of a structure ., can, however, sometimes lead to serious errors. Some very nasty traps lie in wait for those who never loo作者: anchor 時(shí)間: 2025-3-30 16:40 作者: CURB 時(shí)間: 2025-3-30 23:17
Book 2013einer kindlichen anthropologischen Entwicklungsstufe stand. Moderne Menschen haben einen um mehrere Entwicklungsjahre h?heren Entwicklungsstand. Dieser Sachverhalt?hat für die?Humanwissenschaften den Stellenwert, den die Evolutionstheorie?für die?Biologie hat.?.
