Proton magnetic resonance study of polycrystalline HCrO2

A proton magnetic resonance study of polycrystalline HCrO2 as a function of magnetic field and temperature is presented. HCrO2 is paramagnetic, and electron paramagnetic dipole as well as nuclear dipole effects lead to line broadening. The lines are asymmetric and over the range of field 470H09400 gauss and temperature 77°T294°K the asymmetry increases with increasing H0 and decreasing T. An isotropic resonance shift of 0.03% to lower applied fields indicates a weak isotropic hyperfine contact interaction. The general theory of resonance shifts is used to derive a general expression for the second moment M2p of a polycrystalline paramagnetic sample and is specialized to HCrO2. The theory predicts a linear dependence of M2p on [H0(T+)]2, where is the experimentally determined Curie-Weiss constant. The experimental second moment M2p conforms to the relation M2p=(3.960.06)+(0.0840.002)[H0(T+276)]2 in agreement with theory. Hence, the electron paramagnetic effects (slope) can be separated from the nuclear effects (intercept). The paramagnetic dipole effects provide some information on the particle shapes. The nuclear dipole effects provide some information on the motions of the hydrogen nuclei, but the symmetry of the O-H-O bond in HCrO2 remains in doubt.