The Infra-Red Absorption Spectrum of Diborane

Abstract

The infra-red absorption spectrum of diborane has been examined under high resolution from 3.7μ to 30μ with automatic recording grating spectrometers. The rotational fine structure in two bands of each of the three types characteristic of asymmetric top molecules has been measured. All results and observations are consistent with the conclusion that diborane has the bridge structure, and belongs to the same symmetry point group, Vh, as ethylene. The observation and structure of the band with center at 368.7 cm−1 provides spectroscopic evidence that the molecule is non-planar, and makes more definite the assignment of fundamental frequencies. Data on all bands fit quite well the symmetric top approximation, since accidentally two principal moments of inertia are approximately the same, and calculations yield accurate values for certain rotational constants.