Molecular motions in plastic succinonitrile: correlation times from incoherent neutron scattering

Abstract

In the plastic phase (233 K < T < 331 K), the succinonitrile molecule N≡C-(CH₂)₂-C≡N undergoes motions of isomerization between two gauche and a trans conformations and, when in its transform, rotational motions of reorientation from a diagonal of the b.c.c. unit cell to another. After an evaluation of the multiple scattering correction using both a Monte Carlo simulation technique and a semianalytical calculation, the experimental quasi-elastic neutron spectra measured at 302 K were corrected and a comparison is made to a model taking into account the two coupled molecular motions. The correlation times found by fitting this model to the corrected data are: for the rotational motion, and for the reaction of isomerization gauche⇆trans.