Steady-State Nuclear Double Resonance: An Application to the Study of the Quadrupole Resonances of ${\mathrm{K}}^{39}$, ${\mathrm{K}}^{40}$, and ${\mathrm{K}}^{41}$ in KCl${\mathrm{O}}_3$

A steady-state nuclear-double-resonance technique for the detection of low-abundance nuclear-spin resonances has been developed and applied to the detection of quadrupole resonances from ${\mathrm{K}}^{39}$ (93% abundant), ${\mathrm{K}}^{40}$ (0.01% abundant), and ${\mathrm{K}}^{41}$ (7% abundant) in KCl${\mathrm{O}}_3$. From the observed resonances, the ratios of the potassium-nuclei quadrupole moments $\frac{Q_{40}}{Q_{39}}$ and $\frac{Q_{41}}{Q_{39}}$ were found to be 1.244 ± 0.002 and 1.2175 ± 0.001, respectively. Also, the electric field gradient and asymmetry parameter at the potassium sites were measured. In addition, rotary saturation involving the Cl nuclei was observed and studied in very large effective fields corresponding to frequencies up to 600 kHz where the energy absorbed from the saturating fields is extremely small. The steady-state nuclear-double-resonance technique represents a marked improvement over related transient double-resonance techniques. With the steady-state technique, one can gather data at a rate roughly $\frac{T_1}{T_2}$ times greater than that for transient techniques, thereby not only significantly reducing the time required for the measurement of a particular signal, but also lifting very stringent conditons on apparatus stability when $T_1$ is long.