Infrared and Raman spectra and normal coordinate analysis of boranediamine

Abstract

Vibration transition frequencies obtained from moderate-resolution Fourier transform infrared (FT IR) spectra and low-resolution Raman spectra are reported for /sup 11/BH(NH/sub 2/)/sub 2/, /sup 10/BH(NH/sub 2/)/sub 2/, /sup 11/BH(ND/sub 2/)/sub 2/, and /sup 10/BH(ND/sub 2/)/sub 2/. A force-constant refinement calculation using the observed frequencies allows the normal coordinates for the planar modes of boranediamine (BDA) to be determined in terms of 17 independent force constants. One of the two symmetry types of the out-of-plane normal coordinates is determined in terms of four independent force constants. The accuracy of the force field is tested by its ability to reproduce transition frequencies of /sup 11/BD(ND/sub 2/)/sub 2/ and to reproduce observed centrifugal distortion constants of /sup 11/BH(NH/sub 2/)/sub 2/ and observed inertial defects of eight isotopically substituted species of boranediamine. The results are most consistent with a planar structure for the molecule. The B-N stretch force constant is found to be 6.0 mdyn/angstrom and the N-H stretch force constant is 6.8 mdyn/angstrom. These results are consistent with a partial double bond for B-N.