Why spin = 1, 2 species have no electron paramagnetic resonance signal under normal conditions: Possible detection by electron paramagnetic resonance at frequency close to D value?

A universal EPR simulation program has been created by the author, which is based on the following spin Hamiltonian equation: $\text{H = gβB · S + D{S}{}_{\mathrm{z}}{}^2\text{−}\text{S(S + 1)}\text{3}\text{} + E(S}{}_{\mathrm{x}}{}^2\text{− S}{}_{\mathrm{y}}{}^2\text{)}$ where D and e are the axial and rhombic zero-field splitting parameters, respectively. The program can be used for simulation of EPR spectra with half-integer electronic spin ($\text{S =}\text{n}\text{2}$, n = 3, 5, 7, 9) systems. In this article, the integer spin ($\text{S =}\text{n}\text{2}$, n = 2, 4) systems are also considered. The EPR simulation results show that when D > frequency, no EPR signal can be seen from EPR simulation; when D ≈ frequency, whichever X/Q/W-band is used, the EPR signal can be seen on the basis of the simulated EPR results presented.