In situ high-pressure study of ammonia borane by Raman and IR spectroscopy

Abstract

Pressure-induced structural transformations of the ammonia borane complex (NH3·BH3) were investigated in diamond anvil cells by Raman spectroscopy and synchrotron IR spectroscopy up to 14 GPa at room temperature. Starting with a disordered tetragonal structure, NH3·BH3 is found to undergo several transformations upon compression as monitored by in situ Raman measurements. These transformations are indicated by the sequential changes of characteristic Raman modes as well as by the pressure dependence of these modes. Synchrotron IR absorption spectroscopy provided supplementary and consistent information about the structural evolution of NH3·BH3 under compression. Decompression measurements on NH3·BH3 suggest the pressure-induced transformations are reversible in the entire pressure region. The combined Raman and IR data allowed analysis of possible high-pressure structures of NH3·BH3. Our study significantly complements previous high-pressure Raman studies by providing new information on the structures and stabilities of NH3·BH3.