Thermal decay of laser-induced long living metastable electronic states in Na₂[Fe(CN)₅NO] · 2H₂O single crystals

Abstract

We report the thermal decay of extremely long-living metastable states in single crystals of Na2[Fe(CN)5NO] · 2H2O using differential scanning calorimetry. They are generated by laser light in the wavelength range of 350 nm – 580 nm, and their decay was measured in the temperature range of 106 K – 300 K. These states are bulk states which can be generated in molecules with the chemical formula Xn[ML5NO] · yH2O (M = Fe, Ru; L = CN, Cl; X = H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, NH4, Tl, Pb, ZrO, (CH3)4N, C(NH2)3, (CH3)3NCH2COO, CH3NH3. All metastable states decay thermally according to an exponential law. We could not observe any emission of radiation in the energy range of 5 eV – 0.3 eV during the thermal decay. We have evaluated the activation energies EA and frequency factors Z assuming the validity of the Arrhenius law and a first order reaction for three different metastable states (EA1 = 0.70 eV; EA2 = 0.67 eV; EA3 = 0.50 eV; Z1 = 5 × 1015 s−1; Z2 = 5 × 1015 s−1; Z3 = 8 × 1014 s−1). They all can be completely annihilated with red light. A strong temperature dependence with respect to the generation of the metastable states was observed. The energetic position of these states has been estimated by comparison with Mössbauer data and using absorption spectroscopy.