Knowledge Bank

The ESR spectrum of $GdF3$ trapped in solid neon at $4\circ K$ was in accord with its known pyramidal($C3v$) structure and indicated a multiplicity of eight, therefore an $BA1$ ground state. The zero-field-splitting parameter was found to be $|D|=0.435cm-1$ with $g\perp =1.991$ (assuming $g\parallel =ge$). Hyperfine splitting due to $\mathrm{<mrow\; data-mjx-texclass="ORD">155,157</mrow>}$Gd were detected [|$A\perp (155Gd)|=159(6)$ MHz, $|A\parallel (155Gd)|$ = 365(6) MHz], but the $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}F$ hfs was too small to be observed, indicating very ionic bonding. |D| and the $|Ai|$ are large compared to values found for $Gd3+(8s7/2)$ ions in crystalline lattices. The similar, but weaker, spectrum of $GdH3$ yielded $|D|=0.546cm-1$, assuming $g\perp =1.982$ (as for $GdF3$ in solid Ar) and $g\parallel =ge$. The hyperfine constant were $|A\perp (155Gd)|=56(6)$ MHz, $|A\parallel (155Gd)|=69(6)$ MHz, but the hfs due to $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}H$ nuclei was too small to be resolved. The increase in |D| when H replaces F as a ligand is unusual and may indicate that $GdH3$ is planar rather than pyramidal.