Sodium hyperfine splitting

Another intense and complex Mo(V) EPR signal with hyperfine splitting is obtained in D. desulfuricans FDH after anaerobic reaction with sodium formate. This signal is very different from the one observed in other FDHs 224). 

The electron spin resonance (ESR) spectrum of the radical anion of 1,10-phenanthroline obtained by reduction of 1,10-phenanthroline with sodium has been measured, and hyperfine splitting constants were assigned.116... 

Anion-radicals were obtained by alkali-metal reduction of phospholes in ether solvents.602 Sodium and potassium gave radicals rapidly whereas lithium failed. The radicals persisted several days at — 80° but decomposed above - 30°. The persistence of the radicals and their relatively large phosphorus hyperfine splitting, e.g., 186, by comparison with anion-radicals from phosphines, were interpreted in terms of aromatic character.602 The results obtained here contrast with results obtained earlier for 187 where phenyl cleavage and small phosphine-like phosphorus splittings had been observed for the products of attempted anion-radical formation.603 Chemiluminescence on oxidation of the anion-radical of 1,2,5-triphenylphosphole has been reported.604... 

N hyperfine splitting is 13.00 gauss. The radical ion can be made more stable for calibration by making up the aqueous solution in 0.05M sodium carbonate. 

The ketyl radicals of thioxanthen-9-one (166) and -9-thione (167) have been described by several groups, and various ion-pairing phenomena were reported.The hyperfine splittings indicated in gauss, for the ion-pair of 166 with potassium in DME are those of Urberg and Kaiser, and those for the ion-pair of (167) with sodium in the same solvent are due to Aarons and Adam, who found a marked temperature dependence of the counterion hyperfine splittings that indicated is for 23°C. 

Another example of a hydrated salt which gives the stable radicals obtained from C—C bond breakage is sodium perfluorosuccinate hexa-hydrate. When irradiated at room temperature the principal product is OOC-CFa-CF-COO- (28) but at 77°K. the ESR spectrum of CF2COO is also seen (31). In this case the magnitude of the fluorine hyperfine splitting rules out the electron attachment products such as "OOC-CF2-CF COO2" since /3-fluorine splittings are much smaller. In a detailed study of the 77°K. irradiation products of succinic acid (8) only the radical-ion HOOC-CHjj-CHjj-COOH" was mentioned. More recently it is claimed (16) that some of the weak lines are from HOOC-CH CH2 , but HOOC-CH2 has not been reported. 

It should be noted that there is an important distinction to be made between the hexamethylacetone-sodium ion-quartet and the situation described by the original G.F.F. theory. In the G.F.F. theory it was assumed that the solvent dependence of hyperfine splitting constants is to be attributed to modifications in spin density distributions, whereas for the ion-quartet the spin density distribution is the same in tetrahydro-furan and in methyltetrahydrofuran. The variation in with solvent must be due to variation in the geometry of the ion-quartet, which will in turn vary the efficiency of the mechanism whereby spin is transferred to the alkali metal nucleus. Thus, in this case, the solvent dependence is to be attributed to variations in Q rather than p. The situation is common in the study of ionic association through electron spin resonance spectroscopy and has thwarted many attempts at quantitative descriptions of the effect of solvation upon such association until the geometry of the ionic associate in solution is firmly established it is not too rewarding to discuss how the spectrum varies with change in solvent. 

The small magnetic hfs in the E state of a homonuclear diatomic molecule is caused by the interaction of the nuclear spins / with the weak magnetic field produced by the rotation of the molecule. For the Nai molecular ground state the hyperfine splittings are smaller than the natural linewidth of the optical transitions. They could nevertheless be measured by the laser version of the Rabi technique [10.21]. A polarized argon laser beam at A, = 476.5 nm crosses the sodium beam and excites the Na2 molecules on the transition X = 0, 7" = 28) n (v = 3,7 = 27). The hfs... 

The observation of alkali metal hyperfine splitting implies a long-lived complex. Specifically the lifetime of the complex must be greater than or comparable to the reciprocal of the line width (expressed in frequency units). Since the total line width (usually 10 cps) will not entirely be due to the association-dissociation process, it is likely that each anion retains its sodium cation for a time of 10 second or longer. 

A similar change from 9 to 5 lines results sometimes when a simple salt with a common cation is added. In this case reaction (3.2) occurs, so that the lifetimes of the asymmetric units are reduced, but different sodium ions (with varying nuclear spins) are involved, so that the cation hyperfine splitting is lost at the same rate. As usual, at intermediate rates, lines become broad and from the width increments, rates and activation energies and entropies can be obtained. 

The question of the nature of alkali metal clusters in zeolites was first examined by Anderson and Edwards [14], who compared the hyperfine splitting of a series of zeolite-based clusters with a variety of neutral and charged sodium... 

Fig. 8. Percentage atomic character, deduced from a comparison of cluster hyperfine splittings with those of the appropriate free atom (sodium or silver), as a function of the number of atoms (n) for different types of clusters in Na-X (filled squares), Na in solid argon...

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