Postprint version. Published in Chemical Physics Letters, Volume 22, Issue 1, September 15, 1973, pages 124-136.
NOTE: At the time of publication, the author Richard B. Frankel was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1016/0009-2614(73)80549-4.
Mössbauer spectroscopy in external magnetic fields has been used to measure the signs of the principal components of the electric field gradient Vzz in the two forms of [Fe(H2O)6)(Cl04)2. The signs are Vzznegative for low temperature form (A) with quadrupole splitting ΔEA = 3.4 mm/sec, and Vzz positive for high temperature form (B) with ΔEB = 1.4 mm/sec. This implies a trigonally distorted ligand field and the transition (A) → (B) corresponds to compression → elongation with respect to the trigonal axis.