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Intersystem crossing dynamics in Fe(II) coordination compounds

Vef, Andreas
Adler, Peter
Published in Journal of Chemical Physics. 1991, vol. 91, no. 12, p. 8710-8717
Abstract The 5T2(HS)1A1(LS) intersystem crossing rates have been determined for a number of Fe(II) coordination compounds between 10 and 270 K using time-dependent optical spectroscopy. Strong deviations from Arrhenius kinetics with nearly temperature independent tunneling at low temperatures and a thermally activated behavior at elevated temperatures with apparent activation energies smaller than the classical energy barrier were found. The tunneling rates range from ~10−6 s−1 for the doped spin crossover system [Zn1−xFex(ptz)6](BF4)2 to ~106 s−1 for the doped low-spin (LS) system [Zn1−xFex(bipy)3](PF6)2. The large range of 12 orders of magnitude in the low temperature tunneling rates as well as the activated region can be understood in terms of nonadiabatic multiphonon relaxation. Values for the Huang–Rhys parameter S of 40–50 and for the reduced energy gap p of 1–12 are estimated for the present series of compounds. The validity of an inverse energy gap law in the strong vibronic coupling limit with Sp is borne out by experiment.
Keywords Ultralow temperatureVery low temperatureChemical reactionsLow temperatureTime dependenceOptical propertiesArrhenius equationKineticsTemperature dependenceTunnel effectActivation energyPotential barrierDoped materialsSpinZinc compoundsIron compoundsPhosphorus fluoridesEnergy gapInverse problemsVibronic statesCrossing-overLifetimeMetastable statesBoron fluoridesBoron fluorides
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Research group Groupe Hauser
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HAUSER, Andreas, VEF, Andreas, ADLER, Peter. Intersystem crossing dynamics in Fe(II) coordination compounds. In: Journal of Chemical Physics, 1991, vol. 91, n° 12, p. 8710-8717. doi: 10.1063/1.461255 https://archive-ouverte.unige.ch/unige:3045

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