Transition Dipole-Dipole Coupling Between the NO Stretching Vibrations of Nitroprusside Ions in Sr[Fe(CN)5N(16O,18O)].4H2O and Ba[Fe(CN)5N(16O,18O)].3H2O Isotopic Mixtures

S. R. GONZÁLEZ; O. E. PIRO; P. J. AYMONINO; E. E. CASTELLANO

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 1986 vol. 33 p. 5818 - 5824

0163-1829

Abstract. The NO stretching band in the infrared absorption spectra of polycrystalline Sr[Fe(CN)5N(16O,18O)].4H2O and Ba[Fe(CN)5N(16O,18O )].3H2O isotopic mixtures exhibits a fine structure which is not present in the spectra of isotopically normal crystals. These features can be ascribed to isolated light and heavy nitroprusside ions and to clusters integrated by two, three, etc. isotopically alike adjacent complexes. The fine structure of the NO stretching band of O18enriched crystals is described quantitatively in terms of a linear-chain model of [Fe(CN)NO]2- oscillators coupled through harmonic transition dipole-dipole interaction between the strongly polar NO vibrations of nearest-neighboring ions. O16- and O18-containing nitroprusside clusters are assumed to be statistically distributed along the chains. The theoretical frequencies and relative intensities obtained by this model are in fairly close agreement with the observed infrared spectra. In the case of Ba[Fe(CN)5N(16O,18O)].3H2O solid solutions, the vibrations of isolated [Fe(CN)5N 18O]2- ions and pairs and triplets of them are spectroscopically resolved at low temperatures.