Giant lifetimes of optically excited states and the elusive structure of sodiumnitroprusside

Abstract

The properties of sodiumnitroprusside (Na2[Fe(CN)5NO]*2H2O) are investigated by density functional theory. The calculated results both for the free anions as well as for the solid show that the ground-state Born–Oppenheimer surface has local minima for sidewards bonded and inverted NO. The calculated properties for the local minima: very long lifetime because of large barrier, diamagnetism, optical excitation energies, vibrational, and Mössbauer properties are in essential agreement with experiment. The present findings elucidate the possibility of population transfers by illumination with light of different wavelengths.

Mössbauer, nuclear inelastic scattering and density functional studies on the second metastable state of Na2[Fe(CN)5NO]·2H2O

“…yielding as asymmetry is not in accordance with the experimentally determined positive sign [16] and, further, the calculated η is significantly larger than the experimentally observed value of about 0.17(5) [16]. Large asymmetry parameters have also been calculated by Delley et al [11] for a free NP anion (η=0.93) and for the solid with periodic boundary conditions by Delley et al [11] and by Blaha et al [12] A further step of possible dynamic structural disorder includes the view that there are two orientations of the NO group in SII possible that differ by a 90° rotation around the axis perpendicular to the equatorial plane, as observed by X-ray studies [10] and by neutron diffraction studies [23]. Fast dynamic displacement from SIIa, via SIIb, to SIIa' (with the NO group being rotated by 90° with respect to SIIa) yields an averaged EFG tensor,.…”

“…Since the two conformations, staggered and eclipsed, are so close in energy, the question arises, whether the NO group can switch between these two orientations or even freely rotate about the symmetry axis of the anion, as has been suggested by Delley et al [11] and by Blaha et al [12]. Answering this question requires to estimate the energy barrier on the pathway from SIIa to SIIb.…”

“…In contrast, the X-ray diffraction studies of Coppens and coworkers [10] reveal that in the SI state the NO group is inverted and takes the so-called isonitrosyl structure N−C−Fe−O−N, and in the SII state the NO group takes a side-on molecular conformation. Electronic structure calculations, by means of density functional theory (DFT), have been performed with the aim to shed light on the geometrical and electronic structure of SI and SII [11][12][13]. These studies also support the isonitrosyl structure for the SI state and the side-on conformation of the NO group for the SII state.…”

Optical absorption spectroscopy in the metastable state SI of Na2[Fe(CN)5NO]·2H2O

“…The metastable electronic states in single crystals of nitrosyl-compounds like Na2[Fe(CN) 5 NO].2H 2 0 (sodiumnitroprussside, SNP) are of fundamental interest because of their extremely long lifetime oft> 10Ss below characteristic decay temperatures and the reversibility of the excitation process [1]. They can be used for optical information storage with extremely high capacity by volume holography.…”

Characterization of Mixed-Metal Oxides Using Synchrotron-Based Time-Resolved x-ray Diffraction and x-ray Absorption Spectroscopy

“…The measurements at X 19 were performed in the "fluorescence-yield mode", whereas the data at U7A were acquired in the "electron-yield mode". The theoretical spectra for the Mo L-edges [7] were calculated using DFT and commercial versions of the CASTEP [9] and DM013 [10] codes available from Molecular Simulations Inc.…”