Vibrational Spectrum and Force Constants of Diboron Tetrachloride

Abstract
The infrared spectrum of gaseous diboron tetrachloride (B2Cl4) and the Raman spectrum of the liquid are analyzed. The molecular symmetry is shown to be Vd, in accord with the electron diffraction result for the vapor. A complete vibrational assignment is given. The fundamentals are (in cm—1): 1131, 401, 225 in a1; 730, 291 in b2; 917, 617, 180 in e. A normal coordinate analysis, based on a Urey‐Bradley potential function and a least‐squares method of force constant adjustment, is used to establish the assignment. With the aid of the third‐law entropy, the barrier restricting internal rotation about the B–B single bond is fixed at 1700± 600 cal/mole.

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