Gyromagnetic constant

As we shall see, all relaxation rates are expressed as linear combinations of spectral densities. We shall retain the two relaxation mechanisms which are involved in the present study the dipolar interaction and the so-called chemical shift anisotropy (csa) which can be important for carbon-13 relaxation. We shall disregard all other mechanisms because it is very likely that they will not affect carbon-13 relaxation. Let us denote by 1 the inverse of Tt. Rt governs the recovery of the longitudinal component of polarization, Iz, and, of course, the usual nuclear magnetization which is simply the nuclear polarization times the gyromagnetic constant A. The relevant evolution equation is one of the famous Bloch equations,1 valid, in principle, for a single spin but which, in many cases, can be used as a first approximation. 

Shapiro s data for formaldehyde (Table 16) are quite limited, but clearly show a solvent induced decrease for VH D (which is multiplied by the ratio of the gyromagnetic constants of H and D to yield the H—H coupling) going from TMS to acetonitrile. 

This nuclear magnetic moment fl is represented by a vector that is colinear to I and has the same or opposite direction depending on the sign of 7, the gyromagnetic ratio (also called the gyromagnetic constant). 

Gyromagnetic constants of 29Si and 119Sn are negative, in contrast to 207Pb. One-bond ... 

If the primary isotopic effect is neglected, very accurate values may be obtained for the gyromagnetic constant ratio y("7Sn)/y(119Sn) [equation (10)1 from the ratio of the tin resonance frequencies, vTMs(U7Sn)/vTMs(U9Sn)- The ratios of resonance frequencies measured for pairs of tin isotopes with different accuracies by various authors are compared in Table XIV. 

The AC incremental coefficients account for substituent effects (differences with respect to H atoms) in both the central and terminal sites, n,- being the number of counts each particular substitution i occurs. The prefactor K is introduced in order to normaHze the incremental effect on each J-coupling according to the magnitude of the gyromagnetic constants Jx and yy constants of the pair of nuclei involved. 

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