Relative signs

Determination of relative signs of isotropic hyperfine coupling constants J. Chem. Rhys. 63 3515-22... 

The radical cation of 1 (T ) is produced by a photo-induced electron transfer reaction with an excited electron acceptor, chloranil. The major product observed in the CIDNP spectrum is the regenerated electron donor, 1. The parameters for Kaptein s net effect rule in this case are that the RP is from a triplet precursor (p. is +), the recombination product is that which is under consideration (e is +) and Ag is negative. This leaves the sign of the hyperfine coupling constant as the only unknown in the expression for the polarization phase. Roth et aJ [10] used the phase and intensity of each signal to detemiine the relative signs and magnitudes of the... 

From a study (29) of the relative signs of various H, H coupling constants of carbohydrate derivatives it is evident that the couplings... 

The perfectly linear, noise-free relationship between the projections is readily apparent. The slope of each relationship is equal to each proportionality constant Br in equation [65]- Br is sometimes called the inner relationship. The sign of the slope depends on the relative signs of the spectral factor vs. its corresponding concentration factor. 

This equation is the main result needed to explain the effect of the GP on the nuclear dynamics of a chemical reaction. Clearly, the sole effect of the GP is to change the relative sign of and T q. Within each of these functions the dynamics is completely unaffected by the GP. We emphasize that, despite remaining unnoticed for so long in the chemical physics community, Eq. (5) is exact. 

By assuming that the system does not encircle the Cl, Mead showed [14] that this equation implies that the GP changes the relative sign of the inelastic and reactive contributions in the scattering amplitude. 

Feynman paths that loop a different number of times around the Cl are decoupled from one another in the sum-over-paths, with the result that the nuclear wave function can be split into separate contributions from the even- and odd-looping paths. The sole effect of the GP is to change the relative sign of these two components. 

To compare measured magnetic coupling constants with values obtained from theoretical calculations, the signs of the magnetic parameters should be known. In the following, different approaches for the determination of absolute and relative signs of the principal values of hf and quadrupole tensors will be discussed. 

The signs of the three hf principal values A , i = 1, 2, 3, are only determined by the second term in (3.25) which is linear in A. The magnitudes and signs of all Aj can therefore be found by a least square fit of the ENDOR data obtained from different orientations of B0. Since a change of the signs of A and ms does not alter (3.25), only relative signs of Aj can be obtained. 

For nuclei with A > vn, the first term in (3.25) is the dominant one, so that the observed ENDOR frequencies c(ms) are rather insensitive to the signs of Aj. Since the second order term 2 in (3.11) is dependent on the signs of Ay and thus of Aj (3.12), the relative signs of the latter may be found by including higher order contributions in the fitting process. 

Relative signs of the hyperfine splittings of two nuclei. In single crystal ENDOR studies the relative signs between hfs constants of different nuclei may sometimes be determined from the cross-term (3.18). If this second order term between nuclei I and K is... 

If the hfs of the nucleus under consideration is not resolved in the EPR spectrum, all nuclear spin states are simultaneously saturated and a sign determination using ENDOR line intensities is not possible. In this case the relative signs may sometimes be determined from second order hf contributions. This method has been applied by DuVarney and Spaeth74) to determine the sign of the 41K electric quadrupole moment using F centres in KC1. 

DOUBLE ENDOR 4.3 two rf fields 2.5 Separation of overlapped ENDOR spectra, determination of relative signs of hf splittings... 

For nuclei with I > 1, the two ENDOR transitions c( 1/2) are split by the quadrupole interaction. As a consequence, only those EPR transitions which have a level in common with the induced ENDOR transition are observed in the EI-EPR spectrum. This selection of the nuclear spin states reduces the number of lines in the EI-EPR spectrum and allows the determination of the relative signs of hf and quadrupole interactions20,35. ... 

Determination of relative signs of hyperfine interactions. In contrast to the sign determination by DOUBLE ENDOR, spin decoupling can also be applied if the ENDOR signals have no significant transient components (Sect. 4.3). 

Proton ENDOR and DOUBLE ENDOR data on VO(acac)2 in frozen solutions have been reported by van Willigen2895. Since the CH-protons exchange with deuterons in CD3OD they may easily be discriminated from the methyl protons. From the single crystal-like ENDOR spectrum for B0 along g and the two-dimensional powder spectrum at gi, the hf coupling constants Ap 5 = 0.7 MHz and AfHj = 0.7 MHz, A 3 = 1.5 MHz, respectively, have been found. The relative signs of the principal... 

Crepaux, D., Lehn, J. M. Nuclear Spin-Spin Interactions Part IX. Relative Signs of the Geminal Nitrogen-Hydrogen Coupling Constants for Doubly Bonded Nitrogen. Mol. 

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