We thus obtain,
( )
2
2
cos
4
2
4
2
θ
θ
ε
ε
0
0
= −
−
= −
−
′
π
×
π
×
p E
q
q
U
pE
a
a
(2 34)
We note that U¢ (q) differs from U(q ) by a quantity which is just a constant
for a given dipole Since a constant is insignificant for potential energy, we
can drop the second term in Eq