LAMB-MOSSBAUER FACTOR OF ELECTRONICALLY EXCITED MOLECULAR-STATES MEASURED BY TIME-DIFFERENTIAL MOSSBAUER EMISSION-SPECTROSCOPY

The Lamb-Mossbauer Factor (LMF) of molecular crystals is expected to d epend on the electronic molecular states by their different intramolec ular vibrational frequencies. Revisiting Mossbauer spectra obtained by time differential Mossbauer emission spectroscopy of the low spin com pound [Co-57/Mn(bipy)(3)](PF6)(2) (bipy = 2,2'-bipyridine) a ratio of 1.25 for the LMFs of the low spin ground state and of an excited high spin state decaying in the Mossbauer time window could be evaluated. T he difference found is in Line with the change of LMF observed for spi n crossover compounds where the excited high spin state is populated b y the so-called LIESST effect. The initial population of the high spin state is close to 100%.