Normalkoordinatenanalyse und Frequenzberechnungen für die isotopomeren closo-Hydrohexaborate 11Bn 10B6-nH6 2- , n = 0 – 6 / Normal Coordinate Analysis and Frequency Calculations of Isotopomeric closo-Hydrohexaborates 11Bn 10B6-nH6 2- , n = 0 – 6

Abstract

Normal coordinate analyses for the ten isotopomers Cs2 11Bn 10B6-nH6, n = 0 — 6, including the pairs of geometric isomers for n = 2, 3, 4 have been performed, based on a general valence force field. The shift of the bands as well as the splitting of degenerate modes by lowered symmetry due to exchange of 10B by 11B or H by D is exactly calculated by a set of six force constants. The characteristic band patterns observed in the IR and Raman spectra of Cs2B6H6 with natural abundance of B isotopes (80.22% 11B, 19.78% 10B) measured at 10 K are explained by the superposition of the calculated spectra of the different isotopomers present, according to their statistical frequency distribution. The calculated atomic displacements and the potential energy distribution on the symmetry coordinates reveal only a small coupling (PED < 10%) between the cage (in-phase displacements of H and B) and substituent vibrations (anti-phase motions of B and H). Based on the normal coordinate analyses previously obtained assignments for several bands are revised.