ISOMER SHIFT CALIBRATION OF⁵⁷Fe BY LIFE-TIME VARIATIONS IN THE ELECTRON-CAPTURE DECAY OF⁵²Fe.

Abstract

Des mesures de variation de probabilité de capture électronique du 52 Fe dans différents composés de fer permettent d'estimer les densités électroniques au noyau. On en déduit une constante de calibration a pour le déplacement isomérique du 57 Fe : a =-0,31 ± 0,04 a^ .mm.s-1. Abstract.-Electron densities at the nucleus are estimated from measurements of the change in electron capture rate of 52 Fe in different iron compounds. This leads to a calibration constant a for the 57 Fe isomer shift : a =-0.31 ± 0.04 a" .mm.s-1 .

Theoretical 57Fe Mössbauer spectroscopy: isomer shifts of [Fe]-hydrogenase intermediates

“…Further computational savings are possible since spin-orbit coupling can also safely be neglected. Linear correlation plots using effective densities versus experimental isomer shift yield a slope of a = À0.294 a 0 3 mm s À1 (PBE functional) which is in close agreement with experimentally derived 27 isomer shift calibration constant a = À0.31 a 0 3 mm s À1 . Using this correlation constant isomer shifts of very similar quality can be obtained both with and without fitting.…”

“…This value may be compared to the consensus value a = À0.267 AE 0.115 a 0 3 mm s À1 proposed by Oldfield and co-workers 20 based on computational calibration studies, as well as the more recent value a = À0.291 a 0 3 mm s À1 obtained by Wdowik and Ruebenbauer in a series of relativistic solid-state DFT + U calculations using the PBE functional. 26 The a value recommended by Kurian and Filatov was obtained by Ladrie `re et al 27 by combining experimental 57 Fe isomer shifts with differential measurements of the electron capture rate l EC = (ln 2)t EC À1 of 52 Fe in different iron compounds, both being proportional to the contact density. The final value was then obtained by in addition using the measured 28 half-life t EC of 52 Fe as well as the contact density r 0 = 15 070 a 0…”

“…19,20 In this model the isomer shift is calculated directly from 5 using a value of α = −0.31 ± 0.04 a 3 0 mm s −1 from life-time measurements by Ladrière et al 21 At the same time, it was also recommended to employ effective densitiesρ which take into account the finite size of the nuclei. In order to include both relativity and sophisticated computational methods, Kurian and Filatov alternatively proposed 22 to scale non-relativistic effective densities obtained from DFT with a factorρ rel /ρ non-rel computed from CCSD(T) effective density calculations on atomic iron.…”

Density Functional Calculations for Prediction of 57Fe Mössbauer Isomer Shifts and Quadrupole Splittings in β-Diketiminate Complexes

“…The fit values of α are within error of the experimental value of 0.31 ± 0.04 a 0 3 mm s –1 , which has been estimated from the change in electron capture rate of 52 Fe in different iron compounds. 20 …”

Calibration of 57Fe isomer shift from ab initio calculations: can theory and experiment reach an agreement?

“…Besides theoretical calculations, the contact densities can be evaluated from the experimentally measured life times of electron capture by atomic nuclei. Thus, a value of À0.31 AE 0.04 a 3 0 mm s À1 was derived by Ladrie`re et al 15 from the life-time measurements of electron capture by the 52 Fe nucleus. Because the electron capture rate is proportional to the contact density r, the a( 57 Fe) calibration constant could be obtained from a comparison of the measured life times with the 57 Fe isomer shifts in the same compounds.…”