Isotopic coupling

The radical anions of dialkyl sulfoxides (or sulfones) may be obtained by direct capture of electron during y-irradiation. It was shown that electron capture by several electron acceptors in the solid state gave anion adducts 27. It was concluded276 that these species are not properly described as radical anions but are genuine radicals which, formed in a solid state cavity, are unable to leave the site of the anions and exhibit a weak charge-transfer interaction which does not modify their conformation or reactivity appreciably, but only their ESR spectra. For hexadeuteriodimethyl sulfoxide in the solid state, electron capture gave this kind of adduct 278,28 (2H isotopic coupling 2.97 G is less than 3.58 G normally found for -CD3). 

Sputter-Ion Depth Profiling. Although it is essentially a destructive technique, SIMS depth profiling is rapid, and possesses parts per million or even parts per billion sensitivity to all elements and isotopes, coupled with a depth resolution of a few nanometres. Concentration-depth plots can be accurate to 5%. 

Three-pulse ESEEM spectrum of perdeuterated P-carotene imbedded in Cu-MCM-41 exhibits an echo decay with an echo modulation due to deuterons. The three-pulse ESEEM is plotted as a function of time, and curves are drawn through the maximum and minima. From ratio analysis of these curves, a best nonlinear least-squares lit determines the number of interacting deuterons, the distance (3.3 0.2A), and the isotopic coupling (0.06 0.2MHz). This analysis made it possible to explain the observed reversible forward and backward electron transfer between the carotenoid and Cu2+ as the temperature was cycled (77-300 K). 

Conversely, a fairly large inorganic isotope coupling constant such as 1.8 mT for Ga may suggest an unusual oxidation state (here mononuclear Ga ) [56] in a compound 12 where in fact a regular diamagnetic Ga center binds one radical anion and one dianionic a-diimine ligand [57]. 

Harwood K. G., Gillon J. S., Roberts A., and Griffiths H. (1999) Determinants of isotopic coupling of CO2 and water vapor... 

When the line broadening becomes a serious obstacle, one can take advantage of a phenomenon that results in narrower lines. Specifically, substitution of1H atoms with the 2H isotope coupled with 2H NMR spectroscopy results in spectral lines that are up to 40 times narrower than those of corresponding ll NMR, due to slower nuclear relaxation of the 2H nuclei in paramagnetic compounds. 

Nature of Adsorbed Species. - The nature of adsorbed species on the catalyst surface has been largely determined by transient reaction studies (with or without isotopes) coupled with surface spectroscopies during transients such as infrared (IR), Fourier transform infrared (FTIR) and NMR. Various catalysts have been studied including Ni, Ru, Rh, Co, and Fe. 

NMR Studies - The applications of stable isotopes coupled with NMR analysis have multiplied as higher field magnets and sophisticated computer techniques have increased sensitivity, A recent review which discussed NMR studies employing stable isotopes is available. ... 

Compound Ret 6 in ppm (ext Ref CFQa) Coupling constant (Hz) Line width (Hz) Observed isotope coupling ratio Gyro- magnetic ratio... 

Studies of Sr, Pb and Nd isotopes, coupled with trace-element geochemical studies, have shown that the source regions of many continental alkaline volcanics have been enriched in LIL elements, generally some hundreds of million years prior to the beginning of volcanism, and enrichment has been interpreted as due to mantle metasomatism.It has been suggested that mantle metasomatism is a necessary precursor to alkaline continental volcanism.Alkaline rocks erupted in oceanic environments, and even ridge tholei-ites, sometimes bear evidence of source enrichment, which has been interpreted as a result of mantle metasomatism. ... 

It is also usually possible to remove all the couplings from a particular isotope, e.g. H, provided that one only wishes to observe the spectrum from another isotope, e.g. Either the decoupling frequency is noise-modulated to cover the relevant range of chemical shifts, or else the same decoupling is achieved more efficiently, and with less heating of the sample, by using a carefiilly designed, continuous sequence of... 

The simplest system exliibiting a nuclear hyperfme interaction is the hydrogen atom with a coupling constant of 1420 MHz. If different isotopes of the same element exhibit hyperfme couplings, their ratio is detemiined by the ratio of the nuclear g-values. Small deviations from this ratio may occur for the Femii contact interaction, since the electron spin probes the inner stmcture of the nucleus if it is in an s orbital. However, this so-called hyperfme anomaly is usually smaller than 1 %. 

We further make the following tentative conjecture (probably valid only under restricted circumstances, e.g., minimal coupling between degrees of freedom) In quantum field theories, too, the YM residual fields, A and F, arise because the particle states are truncated (e.g., the proton-neutron multiplet is an isotopic doublet, without consideration of excited states). Then, it is within the truncated set that the residual fields reinstate the neglected part of the interaction. If all states were considered, then eigenstates of the form shown in Eq. (90) would be exact and there would be no need for the residual interaction negotiated by A and F. 

Recently, Xu et al. [11] studied in detail the H3 molecule as well as its two isotopic analogues, namely, H2D and D2H, mainly with the aim of testing the ability of the line integral approach to distinguish between the situations when the contour surrounds or does not surround the conical intersection point. Some time later Mebel and co-workers [12,72-74,116] employed ab initio non-adiabatic coupling teiins and the line-integral approach to study some features related to the C2H molecule. 

Concerning N-magnetic resonance, Boejesen et at. (113) have measured the following coupling constants on a sample of thiazole enriched in this isotope ... 

Plasma torches and thermal ionization sources break down the substances into atoms and ionized atoms. Both are used for measurement of accurate isotope ratios. In the breakdown process, all structural information is lost, other than an identification of elements present (e.g., as in inductively coupled mass spectrometry, ICP/MS). 

Accurate, precise isotope ratio measurements are important in a wide variety of applications, including dating, examination of environmental samples, and studies on drug metabolism. The degree of accuracy and precision required necessitates the use of special isotope mass spectrometers, which mostly use thermal ionization or inductively coupled plasma ionization, often together with multiple ion collectors. 

This is the basic process in an inductively coupled plasma discharge (ICP). The excited ions can be examined by observing the emitted light or by mass spectrometry. Since the molecules have been broken down into their constituent atoms (as ions) including isotopes, these can be identified and quantified by mass spectrometry, as happens with isotope ratio measurements. 

Inductively coupled plasmas are used to obtain the ions needed to measure either relative concentrations (amounts) of the various elements in a sample or to obtain accurate elemental isotope ratios. 

Carbon-13 nmr. Carbon-13 [14762-74-4] nmr (1,2,11) has been available routinely since the invention of the pulsed ft/nmr spectrometer in the early 1970s. The difficulties of studying carbon by nmr methods is that the most abundant isotope, has a spin, /, of 0, and thus cannot be observed by nmr. However, has 7 = 1/2 and spin properties similar to H. The natural abundance of is only 1.1% of the total carbon the magnetogyric ratio of is 0.25 that of H. Together, these effects make the nucleus ca 1/5700 times as sensitive as H. The interpretation of experiments involves measurements of chemical shifts, integrations, andy-coupling information however, these last two are harder to determine accurately and are less important to identification of connectivity than in H nmr. 

Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

---