# 5.2: Theoretical Interpretation of CIDEP by the Radical Pair Mechanism

## 5.2 Theoretical Interpretation of CIDEP by the Radical Pair Mechanism

In this section, we will see how CIDEP can be generated from the radical pair mechanism. The spin polarization ( *P*) of ESR transition is represented as shown in Fig. 5-1. Here, *P* is given as follows:

Figure 5-1: ESR signals in (a) absorption and (b) in emission.

The population of the *i*-th level is denoted by *n _{i}*(

*i*= ? or ?), which is represented by

In Eqs. (5-2) and (5-3), *N* is the total number of electron spins and < *S _{z}*> is the net

*z*-component of the spins. Eqs. (5-2) and (5-3) are reasonable because

*n*(

_{a}*n*

_{ ?}) becomes

*N*or 0 (0 or

*N*) when <

*S*> is 1/2 or ?1/2. From Eqs. (5-1) (5-3),

_{z}*P*can be given as follows:

Problem 5-1 | Calculate the P < P (enhanced absorption) or _{eq}P > 0 (emission) as shown in Fig. 5-1. |

Answers

Problem 5-1 | From Eq. (2-8), the Zeeman splitting is equal to the energy of an applied microwave ( |