The vibrational spectrum of solid ferrocene by inelastic neutron scattering

We calculate the spectrum of internal vibrations of a single ferrocene Fe(C 5H5)(2) molecule using ab initio density functional theory (without free pa rameters) and compare this with inelastic neutron scattering data on ferroc ene in the solid state at 28 K. Due to the good agreement, we can assign ea ch vibrational mode to each observed peak in the neutron spectrum and so re move ambiguities existing in the literature. There is also consistency betw een the calculated potential energy of a single ferrocene molecule for diff erent orientations, Phi, of the two cyclopentadienyl C5H5 rings with respec t to each other, which shows a potential barrier of 0.9 kcal/mol, and elect ron diffraction, and between the calculated shallow minimum at Phi=9 deg an d x-ray diffraction. (C) 2000 American Institute of Physics. [S0021-9606(00 )50424-3].