The librationndash;vibration bands of the ammonium ion in ammonium tetraphenylborate: Evidence for nearly free rotation

摘要

The Nndash;H stretching and Hndash;Nndash;H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care. The stretching bands show rotationhyphen;like structure that we attribute to rotational motion of NH+4in a very low barrier. The barrier has the symmetry of a tetrahedral molecule in a tetrahedral site and is characterized by the dimensionless parameter bgr;=1. TheJ=0 andJ=1 levels are below the barrier and theJ=2 levels are above it. Slow interconversion of nuclear spin species is seen in keeping with the low barrier model. The spectra of the ATPB with some NH3D+, with a high concentration of K+and with deuterated phenyl groups have been examined, and show spectra in keeping with the model.