Investigation of the metastable state of Na 2[Fe(CN) 5NO] · 2H 2O by optical spectroscopy I. Comparison of the Raman spectra of the ground and metastable state

Abstract

When excited by the 514.5 nm radiation of an argon ion laser at temperatures below 150 K crystalline sodium nitroprusside Na 2[Fe(CN) 5NO] · 2H 2O can be transformed into an extremely long-living metastable state. The Raman spectra of the crystal in the metastable state and ground state are compared in the range of 50–2350 cm -1. In the metastable state the ṽ(NO)-stretching vibration is shifted by more than 100 cm -1 to smaller frequencies depending on the orientation of the sample with respect to the crystallographic axis. This indicates the population of the antibonding π ∗(NO)-orbital. In addition two new vibrations appear at 566 and 422 cm -1. The other vibrational frequencies of the molecular ion [Fe(CN) 5NO] 2- are scarcely shifted, but relative intensities change.