Theory of Dipolar Lineshifts in Free-Radical Crystals

Abstract

The spin absorption spectrum of a free‐radical crystal containing several inequivalent radicals per unit cell is obtained in the high temperature and the large magnetic field limit. A direct, approximate solution of the total (Zeeman+dipolar) Hamiltonian is used rather than a moment calculation. The spectrum is found for arbitrary ${\omega }_d\mathrm{\hspace{0.17em}/\hspace{0.17em}\Delta \omega }$ where ${\omega }_d$ is the dipolar coupling between radicals whose Larmor frequencies differ by $\mathrm{\Delta \omega }$ . For both small and large ${\omega }_d\mathrm{\hspace{0.17em}/\hspace{0.17em}\Delta \omega }$ , the dipolar lineshifts agree with results based on the moment method.