Effect of Pressure on the Mössbauer Resonance in Ferrocene and Pyrite

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Abstract
The effect of pressure to 200 kbars has been measured on the Mössbauer resonance in ferrocene and pyrite. For both compounds a large increase in s‐electron density at the iron nucleus with pressure was observed. For ferrocene, calculations showed that the increase is primarily due to decrease in shielding of the 3s electrons by the 3d. To account for the change quantitatively it would be necessary to consider the change both in the occupation and radial extent (shape) of the 3d orbitals. The quadrupole splitting in pyrites increased with pressure. Although both qlat and qval are probably important, the results could be accounted for in terms of the former component only. For ferrocene a decrease in quadrupole splitting with increasing pressure was observed. A Wolfsberg—Helmholz type calculation gave a change in electric field gradient which accounted for the effect. The same calculation accounted for the change of the optical absorption frequency with pressure which was previously observed for the e2g→e2g* transition.