ABSTRACT
All paramagnetic compounds possess an unpaired electron, whose interactions with external magnetic eld and with electron and nuclear spins are generally described by the Hamiltonian:
H = - - -
= å òg g g g y q y te e e p m a x r x d i
iB S I SI0 1
1 3 i * ( )
cos ( ) , (2.1)
where γe and γp are the gyromagnetic ratio for electron and proton, respectively ℏ = h/2pi is the Planck constant S is the electron spin operator Ii is the ith term of nuclear spin operator a = 1/3(Axx + Ayy + Azz) is an isotropic hyperne interaction (HFI) constant
with the main terms Aij θ is the angle between the external magnetic eld B0 vector and r vector,
which is the vector between dipole moments of electron spin and the ith nucleus
x is the electron spin coordinate ψ(0) is a wave function proportional to a probability of the localization (or
the density) of an unpaired electron near the interacting nucleus
The a value is not equal to zero only for the electrons, possessing a nonzero spin density ρ(0) = [ψ(0)]2, that is, for s-electrons.
