Extremely Long-Living Metastable State of ${\mathrm{Na}}_2$ [Fe${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_5$NO] · 2${\mathrm{H}}_2$O Single Crystals: Optical Properties

Below 160 K, crystalline ${\mathrm{Na}}_2$[Fe${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_5$NO] · 2${\mathrm{H}}_2$O is transformed into an extremely longliving metastable state ($\tau >{10}^7$ sec) by irradiation with 400-540-nm light. At $T>\mathrm{}160\mathrm{}$ K and by irradiation with red light the new state decays exponentially. During population the transmission of the crystal shows characteristic time behavior with wavelength-dependent saturation. Raman spectra show the coexistence of the ground and metastable states. New infrared and visible absorption bands are interpreted in terms of an energy scheme of the metastable state.