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Vibrational study of the dynamic disorder in nickelocene and ferrocene crystals
Author(s) -
Chhor K.,
Lucazeau G.,
Sourisseau C.
Publication year - 1981
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250110308
Subject(s) - raman spectroscopy , chemistry , intermolecular force , neutron scattering , enthalpy , raman scattering , atmospheric temperature range , molecular vibration , activation energy , spectral line , crystallography , scattering , thermodynamics , molecule , physics , optics , organic chemistry , astronomy
Raman and infrared spectra (10–400 cm −1 ) of Ni(C 5 H 5 ) 2 , Fe(C 5 H 5 ) 2 and of their perdeuterated derivatives ( d 10 ) have been recorded in the 30–300 K temperature range. A new assignment for some internal modes is proposed. The temperature dependence of the low frequency spectra (10–200 cm −1 ) and quasi‐elastic neutron scattering results are discussed in terms of dynamical disorder coming from molecular conformational fluctuations. The elastic incoherent structure factor (EISF) measured from neutron scattering on Ni(C 5 H 5 ) 2 is compatible with 2π/5 ring jumps involving an activation energy of 1.5 kcal mol −1 , while Raman band broadenings are interpreted in terms of large amplitude torsional motions associated with an activation energy of about 0.5 kcal mol −1 . A qualitative representation of the potential driving the torsional motion is proposed and it is pointed out that the intermolecular potential plays an important role. Finally, although the conformational fluctuations can be responsible for the pretransitional effects, they take part only for 15% of the enthalpy variations in the phase transition of Fe(C 5 H 5 ) 2 .