Single crystal spectral studies

In NMR, the field Ho is either an applied (external) field or the hyperfine field. In the former case the NMR spectrum consists of a number of transitions whose frequencies are functions of i/ and 0 when a single crystal is studied. With polycrystalline (powder) samples, a spectral distribution is obtained, the principal features of which are determined by the conditions ... 

Germanium metal is also used in specially prepared Ge single crystals for y-ray detectors (54). Both the older hthium-drifted detectors and the newer intrinsic detectors, which do not have to be stored in hquid nitrogen, do an exceUent job of spectral analysis of y-radiation and are important analytical tools. Even more sensitive Ge detectors have been made using isotopicahy enriched Ge crystals. Most of these have been made from enriched Ge and have been used in neutrino studies (55—57). 

Analogous to the DuP 747 study, complete crystallographic information was not possible on the fosinopril sodium polymorphic system [25], Two known polymorphs (A and B) were studied via a multidisciplinary approach (XRD, IR, NMR, and thermal analysis). Complementary spectral data from IR and solid state 13C NMR revealed that the environment of the acetal sidechain of fosinopril sodium differed in the two forms. In addition, possible cis-trans isomerization about the CgN peptide bond may exist. These conformational differences are postulated as the origin of the observed polymorphism in fosinopril sodium in the absence of the crystallographic data for form B (single crystals not available). 

The roots of the same plant has yielded one new alkaloid together with two known compounds lycoctonine and lappaconitine. The structure of the new alkaloid (cochlearenine) (11) is quite similar to that of cochleareine (9). Due to this resemblance the stracture determination of the compound 11 was carried out not only by spectral data but also by single-crystal x-ray diffraction studies [19]. 

Purines. - A study of anhydrous deoxyadenosine (compound iv) single crystals x-irradiated (70 kGy) and investigated at 10 K found four base radicals (21-24) and one deoxyribose radical (25) (see p. 251).20 Radical 21, a de-protonated electron loss product, was stable to 100 K and readily photobleached at 10 K. Its nitrogen hyperfine coupling tensors were estimated by using values that resulted in acceptable EPR spectral simulations these were A(N10) = (1.76, 0, 0) mT, A(N3) = (0.99, 0, 0) mT and A(N1) = (0.34, 0, 0) mT. 

The literature of the vibrational spectra of adsorbed alkynes (acetylene and alkyl-substituted acetylenes) is very much in favor of single-crystal studies, with fewer reported investigations of adsorption on oxide-supported metal catalysts. Fewer studies still have been made of the particulate metals under the more advantageous experimental conditions for spectral interpretation, namely, at low temperatures and on alumina as the support. (The latter has a wide transmittance range down to ca. 1100 cm-1.) A similar number of different single-crystal metal surfaces have been studied for ethyne as for ethene adsorption. We shall review in more detail the low-temperature work which usually leads to HCCH nondissociatively adsorbed surface structures. Only salient features will be discussed for higher temperature ethyne adsorption that often leads to dissociative chemisorption. Many of the latter species are those already identified in Part I from the decomposition of adsorbed ethene. 

Investigations of the electronic structure of quadruply bound dimers have relied heavily on electronic spectra to reveal the nature of the excited-state configurations. The availability of quantitative molecular orbital calculations coupled with single-crystal polarized electronic absorption spectral studies of quadruply bound dimers at low temperature has firmly established certain features of the excited electronic states of these compounds. A discussion of electronic spectra follows and a tabulation of energies associated with 6 - 6 transitions in quadruply bound dimers is given in Table 111. 

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