THE POPULATION AND STRUCTURAL CHANGES OF THE METASTABLE STATE II IN SODIUMNITRO-PRUSSIDE (Na₂[Fe(CN)₅ NO] 2[[dotaccent]]H2O) AT 60 K. J.Schefer(*), T. Woike(**), S. Hauss hl(**), T. Fernandez(***) and G. McIntyre (***) (*) Laboratory for Neutron Scattering ETHZ+PSI, Paul Scherrer Institute, CH 5232 Villigen PSI, Switzerland (** Institute for Kristallographie,) University at K ln, D 50764 K ln, Germany (** Institute Laue Langevin ILL, Rue des *) Martyres, F-38042 Grenoble Cedex, France

Long-living metastable states are of fundamental interest for information storage and for the investigation of the correlation between electron density, chemical bond and structural behavior. This is of special interest as such systems can be used for holographic data storage yielding storage densities of up to 10 GByte/cm³.

We present population dynamic and structural properties of the metastable electronic exited state MS_II in nitroprusside [Fe(CN)₅ NO]_2-. The population of MS_II was performed in a two step process: Firstly by irradiation with light of =476.5nm in order to excite MS_I by about 50% and secondly by irradiation with light of = 1064 nm to transfer 30% of the anions from MS_I to MS_II. The population is determined by M ssbauer spectroscopy in dependence on light exposure. Structure analysis of a single crystal with 30% of the anions in MS_II and 70% in the ground state has been done using neutron single crystal diffraction.