Knowledge Bank

High frequency EPR spectroscopy is a powerful tool for revealing the magnetic resonance properties of Nickel(II) complexes with an $S=1$ (triplet) ground state. For Ni(ethylenediamine)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}(NO3)2$ we observed first-order spectra at 95 $GHz$. A single crystal of this compound snows two normal $Ms=0\leftarrow Ms=-1$ and the $Ms=—1\leftarrow Ms=0$ transitions with an effective zero-field splitting depending on the orientation in the magnetic field. Moreover, a direct transition that corresponds to $Ms=1\leftarrow Ms=-1$ is observed. For this transition, the intensity is strongly orientation dependent. At the magic angle all three transitions fall on top of each other for this axially symmetric crystal. All three transitions show the same dependence on microwave power. The existence of a two quantum jump ($\Delta Ms=2$ transition) and its dependence of the microwave power cannot be understood and explained in a (conventionally used) 2-level picture of each transition in a triplet system. In the current work we present the results of a 3-level density matrix calculation. The calculation starts from the general equation of motion of the density matrix operator in the Heisenberg $picturea$. The resulting set of differental equations is solved numerically. The solutions reproduce very well the observed linewidths and intensities. The two quantum jump follows intrinsically form the model.