Vibrational Analysis of Substituted and Perturbed Molecules. II. Planar XY3 Molecules; Application to BCl3–HBCl2–DBCl2

Abstract

The vibrational frequencies of isotopically substituted planar XY₃ molecules have been obtained using the Green's function and partitioning techniques. Taking HBCl₂ as an ``isotopic'' species of BCl₃, we have calculated its spectrum, without invoking a force constant model. The excellent agreement between predicted and observed spectra indicates that even the force constant changes may be neglected as a first approximation. Using the information provided by the calculations, we have observed and identified five of the six HBCl₂ fundamentals: ν₁ = 762 and 740 cm^—1, ¹⁰B— and ¹¹B–Cl symmetric stretches; ν₂ = 2617 cm^—1, B–H stretch (no splitting); ν₄ = 1100 and 1089 cm^—1, ¹⁰B— and ¹¹B–Cl asymmetric stretch; ν₅ = 892 cm^—1 (¹¹B only), in‐plane H deformation; and ν₆ = 795 and 784 cm^—1, out‐of‐plane deformation. Frequencies observed and identified for the deuterated compound are: ν₂ = 1969 cm^—1, B—D stretch; and ν₆ = 661 and 645 cm^—1, ¹⁰B–¹¹B splitting. The calculations also indicate that the other frequencies we have not observed are hidden by BCl₃ bands, and that ν₃, a B–Cl bending mode is, at ≈285–290 cm^—1, outside the range of our instrument.