STRUCTURAL PHASE-TRANSITIONS AND MOLECULAR-DYNAMICS IN BORNYL CHLORIDE

Neutron scattering and H-1 NMR investigations of solid DL-bornyl chlor ide have been performed over temperatures from 300 K down to 10 and 10 0 K, respectively. Neutron diffraction patterns showed clearly the exi stence of two structural phase transitions at 230 and 163 K. The inela stic incoherent neutron scattering spectra obtained from the low-tempe rature phase III showed well-separated bands of the lattice and intern al vibrations. Above 163 K, these smeared-out bands and quasielastic s cattering attest to fast stochastic reorientation of protons in the pl astic phases II and I. The temperature dependence of the proton spin-l attice relaxation time reveals discontinuities at the temperature corr esponding to the phase transitions. The activation parameters for rota tion 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 pha se II, and molecular tumbling in phase I, are also given.