https://doi.org/10.1007/s100510050995
Mössbauer study of the vibrational anisotropy and of the light-induced population of metastable states in single-crystalline guanidinium nitroprusside
1
Sofia University, Faculty of Physics, Department of Atomic Physics, 5 James Bouchier
Blvd., 1126 Sofia, Bulgaria
2
Medizinische Universität zu Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
Corresponding author: a trautwein@physik.mu-luebeck.de
Received:
15
December
1998
Revised:
3
March
1999
Published online: 15 November 1999
Mössbauer studies were performed on single crystals of guanidinium nitroprusside with
different orientations of their principal crystallographic axes
with respect to the incident radiation.
The markedly
anisotropic Lamb-Mössbauer factor
, i.e.
is in contrast to that of nitroprussides with
inorganic anions. The observed anisotropy is ascribed to the anisotropic vibrational
mean-square displacement of the nitroprusside anions as a whole which is due to the
specific packing of both, anions and cations, as well as the very weak chemical
bonding between the ions, typical only for guanidinium nitroprusside. The
vibrational anisotropy of iron atoms in barium nitroprusside that has been observed
by X-ray structural investigations has a different origin and therefore does not
result in an anisotropic Lamb-Mössbauer factor. We have also investigated metastable
states in guanidinium nitroprusside that have been populated by means of incoherent
irradiation from light-emitting diodes. With a specific orientation of the guanidinium
nitroprusside single crystal a population of the metastable states up to 26%
could be achieved. Populations of comparable size on lithium, sodium and potassium
nitroprussides have only been reached using coherent laser irradiation.
PACS: 63.20.Dj – Phonon states and bands, normal modes, and phonon dispersion / 76.80.+y – Mössbauer effect; other γ-ray spectroscopy / 39.30.+w – Spectroscopic techniques
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999