Diffuse background

It is important to note that expression (23) can be applied to the crystalline phase intensities only if we include, in the first integral, its own smooth diffuse background and not just the intensity belonging to the crystalline peaks. In fact, a pure crystalline sample also has a smooth background due to the incoherent inelastic scattering (i.e. Compton scattering), the TDS, disorder scattering and, very often, unresolved tails of overlapped peaks. 

An expression including the diffuse background of a crystalline phase was calculated for a Bragg-Brentano geometry [55] ... 

The classical treatment of diffuse SAXS (analysis and elimination) is restricted to isotropic scattering. Separation of its components is frequently impossible or resting on additional assumptions. Anyway, curves have to be manipulated one-by-one in a cumbersome procedure. Discussion of diffuse background can sometimes be avoided if investigations are resorting to time-resolved measurements and subsequent discussion of observed variations of SAXS pattern features. A background elimination procedure that does not require user intervention is based on spatial frequency filtering (cf. p. 140). 

What happens, if the surface of the domains becomes increasingly roughened In this case the shape of the diffuse tail of the SAXS is, again, modified. According to Ruland [140,142] an additional diffuse background is emerging. 

Cosmic chemical evolution and diffuse background radiation... 

As was mentioned in Section 12.1, there is a relationship between metal production and diffuse background radiation, perhaps more properly referred to as extragalac-tic background light (EBL), shown in Fig. 12.1, since most or all of it comes from individual galaxies. 

Discovery of y-rays from Galaxy and diffuse background. 

Mattila, K Leinert, Ch. Schnur, G. 1991, in B. Rocca-Volmerange, J.M. Deharveng J. T. T. Van (eds.), The Early Observable Universe from Diffuse Backgrounds, Gif-sur-Yvette Ed. Frontieres, p. 133. 

Atoms are not rigidly bound to the lattice, but vibrate around their equilibrium positions. If we were able to look at the crystal with a very short observation time, we would see a slightly disordered lattice. Incident electrons see these deviations, and this, for example, is the reason that in LEED the spot intensities of diffracted beams depend on temperature at high temperatures the atoms deviate more from their equilibrium position than at low temperatures, and a considerable number of atoms are not at the equilibrium position necessary for diffraction. Thus, spot intensities are low and the diffuse background high. Similar considerations apply in other scattering techniques, as well as in EXAFS and in Mossbauer spectroscopy. 

The presence of the central spot (the primary beam) and diffuse rings Idiff from the film support brings significant errors into estimated intensities. The shape of the primary beam feam can be approximated by one of several peak-shape functions such as pseudo-Voigt, Gaussian or Lorentzian [16], The diffuse background can be described by a polynomial function of order 12. Then equation (1) becomes... 

In contrast, non-island adsorption at low coverages gives no extra spots, but a weak diffuse background. 

The experimental evidences for these conclusions derive mainly from low-temperature spectra of isolated molecules in rigid matrices.62,63 The diffuseness observed ranges from a few tenths of a cm-1 to thousands of cm-1. In the case of a relatively simple molecule like naphthalene that has two nearby states (S at 31,680 cm-1, and S2 at 34,420 cm-1) a careful study of the second state shows many relatively sharp lines emerging from a diffuse background.64,65 It appears that these sharp transitions can be associated with vibrational levels of the lower electronic state, and that the intensity is borrowed from the second state by the mixing of vibronic states having different electronic parentage in the Born-Oppenheimer representation. 

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