Isotopic line shifts

The direct proof that H is present in certain centers in Ge came from the substitution of D for H, resulting in an isotopic energy shift in the optical transition lines. The main technique for unraveling the nature of these defects, which are so few in number, is high-resolution photothermal ionization spectroscopy, where IR photons from an FTIR spectrometer excite carriers from the ls-like ground state to bound excited states. Phonons are used to complete the transitions from the excited states to the nearest band edge. The transitions are then detected as a photocurrent. 

The precision of isotope ratio measurement in on-line applications is rather low as mainly caused by the high noise level of sequential ICP-MS instruments and a time dependent isotope ratio shift caused by the time depending elution signal of IC and the different times at which the masses for isotope ratio determinations are measured [ 24 ]. 

Lanthanides have isotopes which may used in this technique. The principle consists of measuring resonant y-ray absorption as a function of relative velocity between the source and the sample. The spectral line shifts and splittings give information on the chemical nature and symmetry of the site of ion. Eu3+-transferrin [53] and tumor metabolism studies [54] with 153Sm have not proved to be particularly informative. 

This very simple case is rare because of the small wavelength shifts involved but has been observed for mercury-202 [235]. A cooled low-pressure mercury-202 microwave source and a low-pressure mercury vapour atom cell were used, to ensure minimal line broadening (0.0002 nm at the 253.7 nm line). Only mercury-202 and mercury-200 could be determined in this way, as the other isotopic lines showed overlap, and even this was only possible as, for mercury, low-temperature, low-pressure atom cells can be used. 

Figure 6 111.9MHz Sn NMR spectrum of l,l-dimethyl-2,2-bis-(trimcthyl-stannyl)hydrazine (2S°C 2S% in C () recorded by the refocused INEPT pulse sequence with H decoupling and Hahn-echo (HEED) extension [20] (Hahn-echo delay 0.16 s), showing the reduced intensity of the parent line, allowing the straightforward assignment of the N satellites (marked by asterisks /(" Sn, N)=4S.SHz) and the measurement of the isotope induced shift A / N(" Sn) = —0.0365 ppm...

Most of the lanthanides have isotopes suitable for Mossbauer spectroscopy, c/., e.g., Wertheim (1964). In such experiments the resonant y-ray absorption is measured as a function of the relative velocity between the source and the sample. Spectral line shifts and splittings are related to the chemical nature and symmetry of the site of the ion. Spartalian and Oosterhuis (1973) have examined the spectrum of the Eu -transferrin complex. A single unshifted line was observed, which by itself offers little information. This is because at the low temperature (4.2 K) at which such experiments are normally carried out, only the ground-singlet level, of Eu is populated and it is hardly affected by the environment. Mossbauer spectra of other members of the lanthanide series should be more informative. 

We have seen that the effect of a full or partial deuteration of the cation not only leads to line shifts but also significantly changes the intensities and modifies the assignment of the infrared signatures of the different isotopologues. This is due to the soft, anharmonic, and coupled potential of the Zundel cation, where the dynamics and spectroscopy are strongly dominated by Fermi resonances between various coupled zeroth-order vibrations. The discussed quantum dynamical calculations represent an important milestone in our understanding of the spectroscopy and dynamics of protonated water clusters and on their dramatic isotope effects [41], and could only be achieved after a full-dimensional quantum dynamical treatment of the clusters. 

Table 17.5 Isotopic chemical shifts (8 iso, ppm), line widths (L.W., ppm) and relative intensities (Int, %) as deduced from the reconstruction of the H- Si CP-MAS NMR spectra of pristine and fluorinated silica and line assignments...

Emission spectrometry is generally thought of as a technique for elemental determinations, with isotope ratio determinations being the domain of mass spectrometry. In the manufacture, handling, and analysis of nuclear materials, there is considerable need for techniques to determine both elemental and isotopic concentrations of U, Pu, and other actinides in as near an on-line, process control fashion as possible. These elements emit many lines when excited in an ICP, as shown in fig. 9. Edelson and Fassel (1981) point out that some of these lines exhibit isotopic shifts of sufficient magnitude to be separated by a high-resolution monochromator. An example is shown in fig. 16. Separate lines from each isotope are clearly detectable. In these experiments, the fact that actinides are the heaviest elements actually helps resolution of isotopic lines, because the Doppler width of a line decreases as atomic weight increases. The plasma is operated inside a secure containment facility to prevent excretion of actinides into the environment. Since the analytical information is carried by photons, the optical instrumentation for the actual measurement is completely isolated from the radioactive source, so deposition of actinides in the spec-... 

The number of energy levels found to date, with the aid of the Zeeman effect and the isotope shift data, is 605 even and 586 odd levels for Pu I and 252 even and 746 odd for Pu II. The quantum number J has been determined for all these levels, the Lande g-factor for most of them, and the isotope shift for almost all of the Pu I levels and for half of those of Pu II. Over 31000 lines have been observed of which 52% have been classified as transitions between pairs of the above levels. These represent 23 distinct electron configurations. 

In a Mdssbauer transmission experiment, the absorber containing the stable Mdssbauer isotope is placed between the source and the detector (cf. Fig. 2.6). For the absorber, we assume the same mean energy q between nuclear excited and ground states as for the source, but with an additional intrinsic shift A due to chemical influence. The absorption Une, or resonant absorption cross-section cr( ), has the same Lorentzian shape as the emission line and if we assume also the same half width , cr( ) can be expressed as ([1] in Chap. 1)... 

Because of the exceedingly small hyperfine splittings and shifts of resonance lines in Zn Mbssbauer spectroscopy, one should, in principle, consider the SOD shift as arising from different isotopic compositions or even more so from different chemical compositions of source and absorber. Lipkin [57] has derived a general expression for this shift, which the authors of [54] used to estimate a SOD shift for their experiments of A d —0.006 nm s . ... 

Mossbauer resonance of Zn to study the influence of the gravitational field on electromagnetic radiation. A Ga ZnO source (4.2 K) was used at a distance of 1 m from an enriched ZnO absorber (4.2 K). A red shift of the photons by about 5% of the width of the resonance line was observed. The corresponding shift with Fe as Mossbauer isotope would be only 0.01%. The result is in accordance with Einstein s equivalence principle. Further gravitational red shift experiments using the 93.3 keV Mossbauer resonance of Zn were performed later employing a superconducting quantum interference device-based displacement sensor to detect the tiny Doppler motion of the source [66, 67]. 

The isomer shifts in hafnium Mossbauer isotopes usually are of the order of some percent of the line width. Boolchand et al. [168] observed a relatively large isomer shift of -1-0.19 0.06 mm s between cyclopentadienyl hafnium dichloride (Hf(Cp)2Cl2) and Hf metal. From a comparison with Os(Cp)2 and Os-metal, a value of 5 r ) ( Hf) = —0.37 10 fm has been derived, which implies a shrinking of the nuclear radius in the excited 2 state. Figure 7.37 shows some typical spectra for Hf in various hafnium compounds (from [168]). 

Fig. 3. The normalized excitation functions in A2 versus collision energy for the two isotopic channels for the F+HD reaction. The solid line is the result of quantum scattering theory using the SW-PES. The QCT simulations from Ref. 71 are plotted for comparison. The experiment, shown with points, is normalized to theory by a single scaling factor for both channels. Also shown in (a) is the theoretical decomposition of the excitation function into direct and resonant contributions using the J-shifting procedure.

After cocondensation of SiO (1226 cm 1) with alkali metal atoms like Na or K, new bands are detected at 1014 cm 1 (Na) or 1025 cm 1 (K). They can only be attributed to an SiO" anion because of the red shift of the SiO stretching vibration (with respect to that of uncoordinated SiO) and because of different isotopic splittings (28/29/30SiO, Si16/180) [21]. The formation of an ionic species M+(SiO) (M = Na, K) is in line with the results of quantum chemical calculations for the SiO anion (SiO d = 1.49 A, SiO" d = 1.55 A, "electron affinity" SiO + e + 1.06 eV —> SiO") [20]. Taking simple Coulomb interactions into consideration this species is very likely to have a strongly bent structure. The same situation occurs in gaseous NaCN (<(NaNC) = 81.2°) [22],... 

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