Variable-temperature studies of the 4-isopropylphenol crystal structure from X-ray diffraction. Comparison of thermal expansion and molecular dynamics with spectroscopic results.

Crystalline 4-isopropylphenol, C(9)H(12)O, an optically non-linear material, was studied by X-ray diffraction in order to determine its structure at several temperatures in the 95-300 K range. The thermal expansion coefficients have been calculated from the lattice parameters' dependence on temperature. The rigid-body analysis of the anisotropic displacement parameters including the correlation with the internal motion of large amplitude provided the values of the molecular translation and libration tensors at the temperatures studied and was used to characterize the torsional motion of the isopropyl group. The calculated normal modes and internal torsion frequency were compared with the wave numbers at the maximum of bands in the low-frequency Raman scattering, FTIR and inelastic neutron scattering spectra.