NEUTRON-SCATTERING STUDY OF PHASE-TRANSITION IN NORBORNYLENE AND DL-NORCAMPHOR

Neutron diffraction (ND) and inelastic incoherent scattering (IINS) we re performed on solid norbornylene and DL-norcamphor in the temperatur e range from 10 to 290 K. The first-order structural phase transition was observed in norbornylene at ca. 140 K, by both ND and quasielastic scattering (QNS). For DL-norcamphor the ND pattern does not change on cooling, but at ca. 140 K, the QNS indicates a transition in the reor ientations of the molecules. This phase (plastic phase II) persists up to liquid-He temperatures. Upon heating above 100 It, a new structure , phase III, appears in the ND pattern. Phase III is stable at low tem peratures up to 160 K and, upon further heating, it transforms into ph ase II. The IINS spectra measured at 12 K suggest that the phase III i s more densely packed than phase II. (C) 1998 Elsevier Science B.V. Al l rights reserved.