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

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.