Molecular Motion Anisotropy as Reflected by a "Pseudosolid" Nuclear Spin Echo: Observation of Chain Constraints in Molten<i>cis</i>-1, 4-Polybutadiene

Abstract

A nuclear spin echo ("pseudosolid echo") analogous to a "solid echo" is predicted to be observed even within the motional-narrowing approximation, whenever the molecular motion symmetry gives rise to a nonzero average dipolar spin coupling. It is considered as a new characterization of molecular motion anisotropy. New features are discussed. They are well illustrated by "pseudosolid echoes" observed, for the first time, on protons bound to long chains in a molten polymer system. Echoes are shown to reflect chain constraints.