Electron nuclear double resonance of the divalent europium ion

Abstract

The electron nuclear double resonance spectrum of both isotopes $^{151}$Eu and $^{153}$Eu has been measured in a single crystal of calcium fluoride containing about 0.01% Eu$^{2+}$. As the lines were narrow ($\sim$ 10 kc/s) the hyperfine structure parameter and the nuclear g-value were measured to high precision giving the following values: \begin{align*}A^{151} &= -102.9069 \pm 0.0013 Mc/s, A^{153} &= -45.6730 \pm 0.0025 Mc/s,\\ B^{151} &= -0.7855 \pm 0.0052 Mc/s, B^{153} &= -2.0294 \pm 0.0068 Mc/s,\\ g^{151}_I &= -7.4969 \pm 0.0020 (x 10^{-4}) \beta, g^{153}_I &= -3.3125 \pm 0.0030 (x 10^{-4}) \beta.\end{align*} In order to fit the measured line positions to the spin Hamiltonian which is usually assumed for the system it was necessary to add small higher-order terms. The results of these measurements are compared with the precise atomic beam measurement on Eu.