Structural phase transitions and molecular dynamics in bornyl chloride

Abstract

Neutron scattering and 1H NMR investigations of solid dl-bornyl chloride have been performed over temperatures from 300 K down to 10 and 100 K, respectively. Neutron diffraction patterns showed clearly the existence of two structural phase transitions at 230 and 163 K. The inelastic incoherent neutron scattering spectra obtained from the low-temperature phase III showed well-separated bands of the lattice and internal vibrations. Above 163 K, these smeared-out bands and quasielastic scattering attest to fast stochastic reorientation of protons in the plastic phases II and I. The temperature dependence of the proton spin—lattice relaxation time reveals discontinuities at the temperature corresponding to the phase transitions. The activation parameters for rotation of the inequivalent methyl group hydrogens around their threefold axis, observed in phase III, are estimated. The activation energy and correlation time for anisotropic reorientation of the molecule in phase II, and molecular tumbling in phase I, are also given.