Isotope shifts and

The existence of isotope shifts and of tunable lasers with narrow Hnewidth leads to the possibHity of separating isotopes with laser radiation (113,114). This can be of importance, because isotopicaHy selected materials are used for many purposes in research, medicine, and industry. In order to separate isotopes, one needs a molecule that contains the desired element and has an isotope shift in its absorption spectmm, plus a laser that can be tuned to the absorption of one of the isotopic constituents. Several means for separating isotopes are avaHable. The selected species may be ionized by absorption of several photons and removed by appHcation of an electric field, or photodissociated and removed by chemical means. 

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). 

TABLE 14. Summary of isotope shifts and 2 7 coupling constants for orga-nolead compounds... 

During recent years DFT methods have been used to reproduce vibrational frequencies and IR intensities (dipole moment derivatives) with high accuracy (scaling factors are close to unity).29,60,61 We therefore used the B3LYP and BLYP functionals to calculate the spectra of la and its isotopomers, and indeed the calculated frequencies, isotopic shifts, and intensities are now in excellent agreement with the experimental values (Fig. 3).62 A careful reexamination... 

The six fundamental vibrational frequencies for SeF and TeFe are given in Table XII (21,37,38,103). Force constants for SeFs, calculated with the frequencies from vapor-phase Raman spectra (21) and using isotope shifts and Coriolis coupling constants as additional data (103), are listed in Table XIII in comparison to TeFg (1,24,104,125,139). 

CrCl2 molecules have been isolated in solid inert-gas matrices and their i.r. spectrum has been recorded 33—1000 cm The isotopic shifts and i.r. selection rules indicate a linear 10°) structure. The d-d spectrum of gaseous CrClj has been discussed in terms of ligand field theory.The heat capacity of anhydrous CrCl3 in the temperature interval 2—20 K has been determined and the sublimation and decomposition pressures of the compound have been recorded. ... 

Observed Frequencies, Apfboximate Description of Modes, and Most Important Internal Force Constants Computed to Fit the Observed s C1 and CI Isotopic Shifts and Assumino Two Different Bond Angles of CIO2F2+ ... 

INADEQUATE spectrum, however, may become difficult, even in the case of smaller molecules At a tertiary carbon for example, three doublets will appear, usually overlapping due to similar coupling constants. Further, isotope shifts and AB effects will remove the 13C — 13C satellites from the shift position of the known 13C 12C signal. Thus, it was not until a second dimension was introduced to the experiment - that INADEQUATE became a practical method of structure elucidation. 

The AB and AX systems of all 13C —13C bonds appear in one spectrum when the INADEQUATE pulse sequence (Fig. 2.48) is applied. Complete interpretation usually becomes difficult in practice due to signal overlapping, isotope shifts and AB effects (Section 2.9.4). A separation of the individual 13C— 13C two-spin systems by means of a second dimension would be desirable. It is the frequency of the double quantum transfer (d e) in Fig. 2.48 which introduces a second dimension to the INADEQUATE experiment. This double quantum frequency vDQ characterizes each 13CA — I3CX bond, as it depends on the sum of the individual carbon shieldings vA and vx in addition to the frequency v0 of the transmitter pulse located in the center of the spectrum if quadrature detection is applied [69c, 71] ... 

The Clemmensen reduction was accompanied by D/H exchange via acid-catalysed enolization of the carbonyl group, resulting in the production of deuteriated compounds 57 and 58 with various numbers of deuterium atoms. The mixture of the compound 59 obtained by the Wolf-Kishner reduction was predominantly labelled at position 2. This has been proved by the 13C-NMR spectrum. Isotope shift and loss intensivity on substituted C(2) carbon signals have been observed54,55. 

It has been shown by mass spectrometry that the deuteration of C60 leads to products richer in deuterium content in comparison to the hydrogenation which instead leads almost exclusively to C60H36 (Taylor 1999 Darwish et al. 1995). However, the spectra in Fig. 7.3 show that C60H36 and its deuterated analogous display the same band pattern apart the discussed isotopic shift and hence it is reasonable to state that C60D36 has been obtained and studied. This observation has been made also by other authors who have used also Raman in addition to FT-IR spectroscopy (Meletov et al 2001). 

Next reviews were dedicated to problems of hydrogen-bonded systems. Hydrogen/deuterium isotope effects on NMR parameters in liquids and solids have been reviewed by Limbach et al.11 Review covers period to 2004 and illustrates the correlation of intermolecular hydrogen-bonded systems geometry and H/D isotope shifts and coupling constants, particularly measured in the solid state and in liquids at low temperature. Several reviews concern the isotope effects on intramolecular hydrogen-bonded systems.12-17 Since that time several new papers dedicated to hydrogen-bonded systems were published, mostly on intramolecular systems.18-24... 

The first step in quadrupole resonance studies is the detection of lines in new compounds and the interpretation of the observed frequencies in the light of the molecular and crystalline structure of the compound. In the second step, physical studies are developed which yield informations on the temperature and pressure effects, on the isotopic shift, and on the Zeeman and Stark effects. 

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. 

A. Huber, Th. Udem, B. Gross, J. Reichert, M. Kourogi, K. Pachucki, M. Weitz, and T. W. Hansch, Hydrogen-Deuterium 15-25 Isotope Shift and the Structure of the Deuteron, Physical Review Letters 80, 468-471 (1998). 

Apart from oxidation reactions using O atoms from O3 as precursor molecules, several oxidation processes in matrices have been performed with S atoms which were generated photochemically from OCS (Hawkins et al., 1985). A very simple but instructive example is the reaction of the high-temperture SiS molecule with OCS. After photolysis, the CO2 analogue molecule SiS2 is formed. The linear structure was deduced from the isotopic shifts and Si/ Si) of the antisymmetric stretching vibration (Schnoeckel and... 

The two maxima at 900 and 850 cm." show little or no isotope shift and occur in the frequency range expected for the asymmetric uranyl stretching mode. It does not seem likely that the 850 cm. band arises from the symmetric U—O stretch activated by site symmetry because the absorption is too strong. Other possibilities are that the uranyl group is not symmetrical, the O—U—O bonds are not collinear, or two different... 

The most important NMR parameters obtained for the hydroxyl protons are chemical shifts (6), vicinal proton-proton coupling constants (3J7hc,Oh), temperature coefficients (AS/7), deuterium-induced differential isotope shifts, and exchange rates ( ex)-119-123 These parameters may provide information on hydrogen bond interactions and hydration as well. Moreover NOEs and chemical exchanges involving hydroxyl groups observed by NOESY and ROESY experiments also add to the number of distance restraints used in conformational analysis. 

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