The Molecular Beam Resonance Method for Measuring Nuclear Magnetic Moments. The Magnetic Moments ofLi63,Li73andF199

Abstract

A new method of measuring nuclear or other magnetic moment is described. The method, which consists essentially in the measurement of a Larmor frequency in known magnetic fields, is of very general application and capable of the highest precision in absolute and relative measurements. The apparatus consists of two magnets in succession which produce inhomogeneous magnetic fields of oppositely directed gradients. A molecular beam of the substance to be studied possesses a sigmoid path in these magnets and is focused on a suitable detector. A third magnet which produces a homogeneous field is placed in the region between the two deflecting magnets. In this strong homogeneous field the nuclear moments are decoupled from other nuclear moments and from rotational moments of a molecule in a ${}_{}{}^1{}_{}{}^{}\Sigma$ state, and precess with their Larmor frequency $\nu =\frac{\mu H}{\mathrm{hI}}$. An oscillating field perpendicular to the homogeneous field produces transitions to other states of space quantization when the frequency of this field is close to $\nu$. If such transitions take place the molecule is no longer focused on to the detector by the subsequent inhomogeneous field and the observed intensity diminishes. The application of the method to the molecules LiCl, LiF, NaF and ${\mathrm{Li}}_2$ is described. The nuclear moments of ${\mathrm{Li}}^7$, ${\mathrm{Li}}^6$ and ${\mathrm{F}}^{19}$ were found to be 3.250, 0.820 and 2.622 nuclear magnetons, respectively.