Normal isotope shift

Table 10.1)/ which is the inverse isotope shift assuming the MW as the isotope mass within the framework of the BCS theory. On the other hand, the D-salt of Cu[N(CN)2]Br has a lower than the H-salt (normal isotope shift).These isotope substitution results have been confirmed not only by resistance measurements but also by the magnetization and/or if penetration measurements. It is noteworthy that the D-salt of Cu[N(CN)2]Br has an exceptionally small volume fraction of magnetization due to superconducting (one order of magnitude lower than that of the H-salt). The C substitution of the terminal ethylene groups has a similar but smaller isotope effect to that of the D substitution. However, C or isotope substitution of other parts of the ET molecule has almost no or a normal isotope effect on 7),. 

Vibrational spectra including Raman data of 3,3-dimethyldiaziridine and its hexadeutero compound were recorded in the gas phase and in the crystalline state. Assuming C2 symmetry and employing isotopic shifts and comparison with azetidine, a classification of bands which regarded 33 normal modes could be given (75SA(A)1509). 

Based both on the determined isotopic shifts and the comparison of the radical IR spectrum with the spectra of various substituted benzenes, the bands have been assigned to the normal modes and the force field of the benzyl radical calculated (Table 8). 

It can be seen from Figures 3.7 and 3.8 that the calculations reproduce very well not only the experimental spectra but also the experimentally observed isotopic shifts indicating a high reliability of the computational method. According to this comparison, definite attribution can be made for even the difficult Raman bands that cannot be assigned based solely on the experimental results. It is, however, necessary to mention at this point that the calculated Raman spectrum provided directly by the ab initio computations correspond to the normal Raman spectrum with the band intensity determined by the polarizability of the correlating vibration. Since the intensity pattern exhibited by the experimentally recorded resonance Raman spectrum is due to the resonance enhancement effect of a particular chromophore, with no consideration of this effect, the calculated intensity pattern may, in many... 

Figure 18 shows the spectrum of C3D6 in the CH deformation region. We would expect the normal isotope effect to shift C—D deformations about 400 cm-1, that is, completely out of this region. Thus, the observed bands are due to C—C vibrations. The band at 1473 cm-1 (with a shoulder at 1460 cm-1) can only correspond to the 1545 cm-1 band in C3H6. The... 

Figure 12. Extent of dissolution and re-precipitation between aqueous Fe(III) and hematite at 98°C calculated using Fe-enriched tracers. A. Percent Fe exchanged (F values) as calculated for the two enriched- Fe tracer experiments in parts B and C. Large diamonds reflect F values calculated from isotopic compositions of the solution. Small circles reflect F values calculated from isotopic compositions of hematite, which have larger errors due to the relatively small shifts in isotopic composition of the solid (see parts B and C). Curves show third-order rate laws that are fit to the data from the solutions. B. Tracer experiment using Fe-enriched hematite, and isotopically normal Fe(lll). C. Identical experiment as in part B, except that solution Fe(lll) is enriched in Te, and initial hematite had normal isotope compositions. Data from Skulan et al. (2002).

The pyramidal structure of symmetry Cg for FCIO2 was also confirmed by vibrational spectroscopy. E. A. Smith et al. (271) and Arvia and Aymonino (6) reported the infrared spectrum of the gas. D. F. Smith et al. (270) studied the infrared spectrum of the gas, measured the 3501-3701 i6Q i8o isotopic shifts, recorded the Raman spectrum of the liquid, and carried out a normal coordinate analysis. The observed frequencies and their assignment are summarized in Table XIII. 

The C—C bond was found to be slightly more perturbed than in the monolithium species (i.e., LiC2H4) and the Li—C interactions somewhat more rigid. The normal coordinate analysis showed that such a model is capable of satisfactorily reproducing the measured isotopic shifts on the observed 12 fundamentals. However, the very important Li—Li vibration, which could prove the proposed geometry, was not detected in the expected far-infrared spectral region ... 

Chalcogenometalate ions are distinguished by characteristic high-intensity absorption bands in the UV-vis region but they can also be traced by IR and Raman spectroscopy. Total assignments and normal coordinate analyses are available for many of the species (also with recourse to isotope shifts, as in the case of MoOjSj-, 92/100MoOS2 or 92,100MoS4-). 

The 1975 publication by Schlapfer and Nakamoto128 appears to be the most recent example of the application to dithiolenes of IR spectroscopy, in this case basing assignments on Ni isotope shifts, coupled with a normal coordinate analysis. An overview of standard IR spectroscopic data on bisand tris-dithiolenes was provided in the review by McCleverty.4... 

The average Mo=0 bond distance of the (MPT)Mo(0)2(S-eys) cofactor of sulfite oxidase is 1.68 A by EXAFS (Figure 14). The RR results are consistent with bis(oxido) coordination of MoVI and the two expected Mo=0 stretching modes are found at 903 and 881 cm-1 [119,139], Upon reduction and reoxidation in the presence of H2180 the Mo=0 bands shift to 890 and 848 cm-1, respectively [119,139], The difference in the 180 isotopic shifts for the symmetric and asymmetric bands is consistent with labeling of only one of the oxido ligands. This observation has precedent in the labeling of bis(oxido) model complexes and is supported by normal coordinate analysis [140],... 

The change in mean-squared-charge radius is obtained from the isotope shift using standard techniques [HEI74]. For thallium the normal mass shift is approximately 8 MHz between masses and the specific mass shift is smaller than the experimental error. The resulting field shift is proportional, to good approximation, to an electronic factor times 6. For the case of T1 the electronic factor is not directly calculable but should be virtually the same for all isotopes. 

Based on the experimental frequencies and isotope shifts, a Quantum-Chemistry Assisted Normal Coordinate Analysis (QCA-NCA) has been performed. Details of the QCA-NCA procedure of I, including the f-matrix and the definition of the symmetry coordinates, have been described previously (12a). The NCA is based on model I (vide supra). Assignments of the experimentally observed vibrations and frequencies obtained with the QCA-NCA procedure are presented in Table II. The symbolic F-matrix for model I is shown in Scheme 3. Table III collects the force constants of the central N-N-M-N-N unit of I resulting from QCA-NCA. As evident from Table II, good agreement between measured and calculated frequencies is achieved, demonstrating the success of this method. 

Results. The experimental 15N isotope effect at N1 for the decarboxylation of OMP in ODCase (Scheme 1) was measured by Cleland et al. to be 1.0068.66 Comparison of this normal isotope effect with IEs measured for the model compounds picolinic acid (17) and A-methyl picolinic acid (18) led Cleland and coworkers to conclude that the normal IE observed for OMP decarboxylation is indicative of the lack of a bond order change at Nl. This conclusion was based on the following reasoning. The IE for the decarboxylation of picolinic acid (17) is 0.9955 this inverse value is due to the change in bond order incurred when the proton shifts from the carboxylate group to the N in order to effect decarboxylation (equation 2) the N is ternary in the reactant, but becomes quaternary in the intermediate, which results in the inverse IE. The decarboxylation of A-methyl picolinic acid (18) involves no such bond order change (equation 3), and the observed normal IE of 1.0053 reflects this. 

Vibrational spectroscopy has not been extensively used in the characterization of tris(dithiolene) metal complexes. Moreover, complete assignments based on both IR and Raman spectra, isotope shifts, and normal mode calculations are not available for any individual complex. However, the available data suggest that the trends in M S and dithiolene ligand vibrational modes as a function of the metal, the charge on the complex, and dithiolene substituents, closely parallel those discussed above for square-plane bis(dithiolene) metal complexes. Accordingly, the vibrational data are consistent with highly delocalized complexes with predominantly ligand-based redox chemistry. 

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