Neutron scattering definition

One of the most intriguing recent examples of disordered structure is in tomato bushy stunt virus (Harrison et ah, 1978), where at least 33 N-terminal residues from subunit types A and B, and probably an additional 50 or 60 N-terminal residues from all three subunit types (as judged from the molecular weight), project into the central cavity of the virus particle and are completely invisible in the electron density map, as is the RNA inside. Neutron scattering (Chauvin et ah, 1978) shows an inner shell of protein separated from the main coat by a 30-A shell containing mainly RNA. The most likely presumption is that the N-terminal arms interact with the RNA, probably in a quite definite local conformation, but that they are flexibly hinged and can take up many different orientations relative to the 180 subunits forming the outer shell of the virus particle. The disorder of the arms is a necessary condition for their specific interaction with the RNA, which cannot pack with the icosahedral symmetry of the protein coat subunits. 

It is noteworthy that the d- values obtained from the electron microscopy experiments are definitely different from those obtained by in situ neutron scattering studies of the gel phase, being much higher for both the c = 0.001 M and c = 0.01 M cases. As we saw in Chapters 1 and 3, the spacings reported for these electrolyte concentrations were 60 nm and 30 nm, respectively, which have to be compared with the present results. The electron microscopy results are greater by a factor between one and a half and two, the discrepancy being outside the range of experimental error. 

There have been several measurements of the lattice dynamics of quartz by inelastic neutron scattering. Early results showed that the soft mode in the high-temperature phase is overdamped (Axe 1971). Other work on RUMs at wave vectors not directly associated with the phase transition showed that on cooling through the phase transition the RUMs rapidly increase in frequency since they are no longer RUMs in the low-temperature phase (Boysen et al. 1980). The most definitive study of the RUMs associated with the phase transition was that of Dolino et al. (1992). 

The pair distribution function leads to the pair correlation function, which illustrates how the local order found near a given molecule is lost as distance from the molecule increases. This quantity is of fundamental theoretical interest and may be determined in X-ray and neutron scattering experiments, as discussed below. The definition of the pair correlation function g r j) is... 

To these purposes, a review of the methods used for the study of lamellar materials will also be included, and indications on how to ameliorate spectral recording to enhance fine details will be given. Nevertheless, we point out that combining XAS with other techniques (e.g., XRD, NMR, neutron scattering, etc.) is still the best way to fully characterize any material at the present time. See Table 1 for definitions of spectroscopic symbols used in this chapter. 

If BD is so crucial, how do we know it exists and can we measure it quantitatively The existence of M - H2 a BD was definitively proven by inelastic neutron scattering measurements of a barrier to rotation of H2, which would not... 

Let us assume that the particles pack as either an ordered hexagonal or face-centred cubic lattice. Both arrays yield identical results in the following analysis. There is definite evidence for the latter from light diffraction and small angle neutron scattering studies (Ottewill, 1980). The case of a hexagonally closed packed array is shown in Fig. 13.6. We will assume the complete absence of defects, which may well be very important in actual compression studies. We will calculate the pressure on one side of a hypothetical plane inserted into the lattice along a slip-plane. 

Input data include solid-state NMR measurements. Eor W(CO)3(P Pt3)2(H2), 7hd is 34 Hz, giving 7hh = 0.86—0.88 A versus 0.89 A from solid-state NMR and 0.82(1) A from neutron diffraction (uncorrected for H2 libration " ). Short Ti values for the H2 ligand are also diagnostic (e-g-, 4 ms for the W complex), although care must be exercised in interpretation. Inelastic neutron-scattering studies of H2 rotation/ libration provide definitive evidence for molecular H2 binding and also H2— M backdonation but are difficult experimentally. 

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