l
l
k
k
M s
M 1
M 1
nv
nA 0
2
H k
H l
H
o
H m
nv
nv
m
m
- 1
2
+ 1
2
+ 1
2
+ 1
2
+ 1
2
- 1
2
- 1
2
- 1
2
- 1
2
- 1
2
nA 0
2
Scheme 4.2 Effect of the
hyperfine interaction for
hydrogen atom
H k ¼ hv 0 =gb À a=2 M I ¼ 1=2
H m ¼ hv 0 =gb þ a=2 M I ¼ À1=2
where a ¼ hA 0 =gb (Scheme 4.2)
4.3.3 The Electronic Interaction with the Magnetic Field
in Oriented Systems
In the most general case, the interaction energy of an electron with the magnetic
field is anisotropic (Figs. 4.8 and 4.9), provided the matter physical status does not
induce averaging of the magnetic interactions. g is represented by a tensor, and the
Hamiltonian operator is
H ¼ b SgH S and H are both vectors
H ¼ b S x g xx H x þ S y g yy H y þ S z g zz H z
À
Á
4.3.4 The Electronic Interaction with the Magnetic Field
in Oriented Systems
g xx , g yy , and g zz are the g components along three directions, called principal
magnetic axes, observed when the magnetic field is oriented along one of these
directions.
4.3 Electron Spin Resonance
77