PNNL

Abstract

Raman spectra of single crystal ammonia borane, NH3BH3, were recorded as a function of temperature from 77 to 300 K using Raman microscopy and a variable temperature stage. The orthorhombic to orientationally disordered tetragonal phase transition at 225 K was clearly evident from the decrease in the number of vibrational modes. However some of the modes in the orthorhombic phase appeared to merge 10 to 12 K below the phase transition perhaps suggesting the presence of an intermediate phase. Factor group analysis of vibrational spectra for both orthorhombic and tetragonal phase is provided. To our knowledge this is first reported vibrational spectra in the BH and NH stretching region of single crystal NH3BH3 in the orthorhombic phase.