K Edge

	K Edge In X-ray absorption spectroscopy, the K-edge is a sudden increase in x-ray absorption occurring when the energy of the X-rays is just above the binding energy of the innermost electron shell of the atoms interacting with the photons. The term is based on X-ray notation, where the innermost electron shell is known as the K-shell. Physically, this sudden increase in attenuation is caused by the photoelectric absorption of the photons. For this interaction to occur, the photons must have more energy than the binding energy of the K-shell electrons (K-edge). A photon having an energy just above the binding energy of the electron is therefore more likely to be absorbed than a photon having an energy just below this binding energy or significantly above it. The energies near the K-edge are also objects of study, and provide other information. Use The two radiocontrast agents iodine and barium have ideal K-shell binding energies for absorption of X-rays: 33.2 keV and 37.4 keV r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	X-ray Absorption Spectroscopy X-ray absorption spectroscopy (XAS) is a set of advanced techniques used for probing the local environment of matter at atomic level and its electronic structure. The experiments require access to synchrotron radiation facilities for their intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids. Background XAS data are obtained by tuning the photon energy, using a crystalline monochromator, to a range where core electrons can be excited (0.1-100 keV). The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively. For instance, excitation of a 1s electron occurs at the metal K-edge, K-edge, while excitation of a 2s or 2p electron occurs at an metal L-edge, L-edge (Figure 1). There are three main regions found on a spectrum generated by XAS data, which are then thought of as separate spectroscopic techniques (Figure 2): # The ''absorption thresho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Electron Excitation Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy. Or it is achieved through collisional excitation (CE), where the electron receives energy from a collision with another, energetic electron. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to transfer electrons to a higher energy band such as a more energetic sublevel or energy level. When an excited electron falls back to a state of lower energy, it undergoes electron relaxation (deexcitation). This is accompanied by the emission of a photon (radiative relaxation/spontaneous emission) or by a transfer of energy to another particle. The energy released is equal to the difference in energy levels between the electron energy states. Excited states in nuclear, atomic, and molecule systems have distinct energ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Metal L-edge Metal L-edge spectroscopy is a spectroscopic technique used to study the Electron configuration, electronic structures of transition metal atoms and Coordination complex, complexes. This method measures X-ray absorption spectroscopy, X-ray absorption caused by the Electron excitation, excitation of a metal 2p electron to unfilled d orbitals (e.g. 3d for first-row transition metals), which creates a characteristic absorption peak called the L-edge. Similar features can also be studied by Electron energy loss spectroscopy, Electron Energy Loss Spectroscopy. According to the selection rules, the transition is formally electric-dipole allowed, which not only makes it more intense than an electric-dipole forbidden Metal K-edge, metal K pre-edge (1s → 3d) transition, but also makes it more feature-rich as the lower required energy (~400-1000 eV from scandium to copper) results in a higher-resolution experiment. In the simplest case, that of a Copper(II) chloride#Coordination complexes, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]