Deuterium location, determination

The structure of [TpBut]ZnH has been determined by x-ray diffraction, although the hydride ligand was not located (Fig. 38). However, definitive evidence for the presence of the hydride ligand is provided by NMR and IR spectroscopies. Specifically, the hydride resonance is observed at 8 5.36 ppm in the H NMR spectrum, and p(Zn-H) is observed as a strong absorption at 1770 cm-1 in the IR spectrum, which shifts to 1270 cm 1 (vhIpd = 1.39) upon deuterium substitution (Fig. 39). 

In Chapter 8, Stavola and Pearton discuss the local vibrational modes of complexes in Si that contain hydrogen or deuterium. They also show how one can use applied stress and polarized light to determine the symmetry of the defects. In the case of the B-H complex, the bond-center location of H is confirmed by vibrational and other measurements, although there are some remaining questions on the stress dependence of the Raman spectrum. The motion of H in different acceptor-H complexes is discussed for the Be-H complex, the H can tunnel between bond-center sites, while for B-H the H must overcome a 0.2 eV barrier to move between equivalent sites about the B. In the case of the H-donor complexes, instead of bonding directly to the donor, H is in the antibonding site beyond the Si atom nearest to the donor. The main experimental evidence for this is that nearly the same vibrational frequency is obtained for the different donor atoms. There is also a discussion of the vibrational modes of H tied to crystal defects such as those introduced by implantation. The relationship of the experimental results to recent theoretical studies is discussed throughout. 

Deuterium sites for Sr2IrDs and Sr2RuDg were located from neutron diffraction studies, and the positions that gave the best fit (24) are summarized in Table II. With these coordinates, bond distances also were determined and are shown in Table III. The transition elements were viewed as six coordinate with respect to deuterium, where the atomic ratios were D Ru = 6 for Sr2RuDe and D Ir = 5 plus one random vacancy for Sr2IrDs. 

The discussion thus far has emphasized sensitivity of the frequency of C02 s v3 mode to local stress, sensitivity of its absorption intensity to IR polarization, and sensitivity of both properties to resonant coupling of dimers. For the type of crystals under consideration, which consist mostly of simple hydrocarbon groups, these factors probably dominate in determining the IR spectral characteristics. Other factors can be involved, however, and although they can make simple interpretation of the spectra more problematic, they can also provide additional information about the environment of the C02 probe molecule. The following examples illustrate how one can track the motion of C02 over distances of 1-15 A by observing its proximity to free radical centers or to halogen or deuterium substituents in the crystal lattice. This information complements the previously discussed structural studies, which related to structure within the dimer rather than to the location of the C02 in the crystal matrix. 

Variation of contrast [46] is an important experimental technique in neutron small-angle scattering. Above and beyond size determination, it affords detailed insights into the internal structure of dissolved dendrimers and even permits the location of selected components of the molecule which have been previously labelled with deuterium. 

The determination of the location of the deuterium atoms in these two compounds was accomplished by the use of infra-red 149> and boron-11 nmr spectroscopy. These techniques also showed that complete scrambling occurred in about 1.3 hours at room temperature and the... 

Deuterium NMR (2H-NMR) is a powerful technique to obtain information on both the degree of order and the molecular dynamics of liquid crystalline media. It has extensively been used on model as well as natural membranes. Deuterium NMR has been used as a probe to investigate chain packing in lipid bilayers, and the effects of hydrocarbons and alcohols and their location in the membrane have been determined [123]. 

Cu isotopes both with nuclear spin I-3/2. The nucle r g-factors of these two isotopes are sufficiently close that no resolution of the two isotopes is typically seen in zeolite matrices. No Jahn-Teller effects have been observed for Cu2+ in zeolites. The spin-lattice relaxation time of cupric ion is sufficiently long that it can be easily observed by GSR at room temperature and below. Thus cupric ion exchanged zeolites have been extensively studied (5,17-26) by ESR, but ESR alone has not typically given unambiguous information about the water coordination of cupric ion or the specific location of cupric ion in the zeolite lattice. This situation can be substantially improved by using electron spin echo modulation spectrometry. The modulation analysis is carried out as described in the previous sections. The number of coordinated deuterated water molecules is determined from deuterium modulation in three pulse electron spin echo spectra. The location in the zeolite lattice is determined partly from aluminum modulation and more quantitatively from cesium modulation. The symmetry of the various copper species is determined from the water coordination number and the characteristics of the ESR spectra. 

The retinal was first thought [60] to be on a lysine, subsequently identified as lysine 41, but later found [58,61-64] to be in a different part of the molecule, on lysine 216. The angle of the absorption vector of the chromophore was determined to be about 23° inclined from the membrane surface [34,65,66], as expected for a linear molecule attached to a helical peptide segment. The position of the retinal in the protein was located from differential neutron scattering by bacteriorhodopsin in which the retinal was labeled with deuterium [67,68]. 

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