ABSTRACT:
H_{2}N has one unpaired electron and three nuclei of non-zero spin. The four H_{2}N isotopes from ^{1}H, ^{2}H, ^{14}N and ^{15}N have corresponding sets of hyperfine interactions. Measurements of these constrain calculations of electronic wavefunctions and energies, and provide basic knowledge for application to more complex systems. Nuclear spin-state mixing arises from the off-diagonal elements of the nuclear energy matrix, e.g. M_{xx} ≡ σκ 〈ψ|Σ (S_{kz}x^{2}_{kn/}r^{5}_{kn }+ S_{k'z}x^{2}_{k'n/}r^{5}_{k'n}|Ψ〉 (Airne and Brill, Phys. Rev.A 63 052511). The principle hyperfine A-values can be expressed in terms of the M’s, e.g. A_{zz} = A_{Fermi} - (4/3σ)( M_{xx} + Myy - 2 M_{zz}), thereby simplifying the energy matrices. In the absence of nuclear spin-state mixing (i.e. each state pure m_{I}) there are, e.g. 10 epr transitions in D_{2}^{15}N and 15 in D_{2}^{14}N, all Δm_{I} = 0 fully allowed. In the presence of mixing there are 243 in D_{2}^{15}N and 729 in D_{2}^{14}N, with large differences in probability among transitions. Because of numerous, at least partially allowed, overlapping transitions, useful information can be obscured in H_{2}N magnetic resonance spectra. Research is required to arrive at effective experimental conditions. The wide range of transition probabilities will cause H_{2}N resonances to exhibit a corresponding range of microwave power saturation behavior. Simulations display remarkable effects which call for experimental verification by employing a wide range of powers. The nuclear Zeeman interaction (proportional to B) perturbs both the energy and state mixing of nuclear levels, thereby affecting the separation and probability of resonances. Of special interest are the fields B_{cross} at which pairs of hyperfine levels draw closest. A spectrometer with microwave frequency scanning at fixed B would be useful for centers like H_{2}N in which on-diagonal hyperfine energy matrix elements depend significantly upon B. |