The infrared spectra of some B 11 labeled diboranes

Abstract

The spectra of B 11 2H 6 and B 11 2D 6 are similar to those of normal diborane; however, there are pronounced differences in band structure, in shape of rotational envelopes, and positions of maxima of bands. With NaCl prism resolution, peaks which should show three separate bands, B 11 2H 6, B 11B 10H 6, and B 10 2H 6, show only one with slight shifts in positions of maxima. These differences are directly related to percent B 10 content. By calibrating an instrument with samples of diborane of known B 10 content, it is possible to determine the boron isotopic composition of diborane to within 1% on an ordinary single or double-beam spectrometer. No vibrations, which should become infrared-active in B 11B 10H 6 because of lowering of symmetry from V h to C 2 v , were observed. Studies employing a grating infrared spectrometer permitted complete separation of B 11 2, B 11B 10, and B 10 2 peaks of ν 14 and ν 18 vibrations for diboranes containing 1.13, 18.83, 56.4, 73.5, and 96% B 10. The resolution was good enough to permit the estimation of the fractions of each of the species B 11 2, B 11B 10, and B 10 2 present in the samples.