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More generally, the term cross-section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagnetic absorption, etc. (Note that light in this context is described as consisting of particles, i.e., photons.) A typical absorption cross-section has units of cm 2 ⋅molecule −1.
The absorption coefficient is fundamentally the product of a quantity of absorbers per unit volume, [cm −3], times an efficiency of absorption (area/absorber, [cm 2]). Several sources [2] [12] [3] replace nσ λ with k λ r, where k λ is the absorption coefficient per unit density and r is the density of the gas.
In physics, the cross section is a measure of the probability that a specific process will take place in a collision of two particles. For example, the Rutherford cross-section is a measure of probability that an alpha particle will be deflected by a given angle during an interaction with an atomic nucleus.
X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter. [1] The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids. [2]
To describe the attenuation coefficient in a way independent of the number densities n i of the N attenuating species of the material sample, one introduces the attenuation cross section = (). σ i has the dimension of an area; it expresses the likelihood of interaction between the particles of the beam and the particles of the species i in the ...
X-ray absorption near edge structure (XANES), also known as near edge X-ray absorption fine structure (NEXAFS), is a type of absorption spectroscopy that indicates the features in the X-ray absorption spectra of condensed matter due to the photoabsorption cross section for electronic transitions from an atomic core level to final states in the energy region of 50–100 eV above the selected ...
The XANES energy region [3] extends between the edge region and the EXAFS region over a 50-100 eV energy range around the core level x-ray absorption threshold. Before 1980 the XANES region was wrongly assigned to different final states: a) unoccupied total density of states, or b) unoccupied molecular orbitals (kossel structure) or c) unoccupied atomic orbitals or d) low energy EXAFS ...
Since EXAFS requires a tunable x-ray source, data are frequently collected at synchrotrons, often at beamlines which are especially optimized for the purpose. The utility of a particular synchrotron to study a particular solid depends on the brightness of the x-ray flux at the absorption edges of the relevant elements.