Hyperfine Structure of 7Li79,81Br by Molecular-Beam Electric Resonance

The molecular‐beam electric‐resonance technique has been used to measure the hyperfine interaction constants of the J=1, v=0 state of ⁷Li^79,81Br in the limit of weak external fields. The results for the bromine and lithium nuclear electric quadrupole interaction constants, eqQ_Br and eqQ_Li, the spin‐rotation constants, c_Br and c_Li, the ``tensor'' nuclear spin‐spin interaction, c<sub>3</sub>, and the ``scalar'' nuclear spin‐spin interaction are (in kilohertz) $$\begin{array}{ccc}& {}^7{\mathrm{Li}}^{79}\mathrm{Br}& {}^7{\mathrm{Li}}^{81}\mathrm{Br}\\ {\mathrm{eqQ}}_{\mathrm{Br}}& \text{38368.104(36)}& \text{32050.860(46)}\\ {\mathrm{eqQ}}_{\mathrm{Li}}& \text{211.04(10)}& \text{211.03(13)}\\ c_{\mathrm{Br}}& \text{7.8816(58)}& \text{8.4740(74)}\\ c_{\mathrm{Li}}& \text{0.859(15)}& \text{0.815(19)}\\ c_3& \text{1.0710(61)}& \text{1.1789(78)}\\ c_4& \text{0.0604(70)}& \text{0.0711(89)}\end{array}$$ A theory which permits the calculation of the optimum power required to drive the hyperfine transitions is presented and experimentally verified. A possible pseudoquadrupole effect is discussed, and recent calculations of molecular electric field gradients are used to determine the nuclear quadrupole moments.