PRINCIPAL COMPONENT ANALYSES OF THE METHYL-CHLORIDE, BROMIDE, AND IODIDE POLAR TENSORS

The isotopic invariance criterion, ab initio molecular orbital calcula tions and principal component analysis are used to determine polar ten sor values from the experimental infrared intensities of methyl chlori de, bromide and iodide. For the A1 symmetry species the preferred dipo le moment derivative sign combinations (+ - -)H (+ - -)D for all three halides are in agreement with previous studies. On the other hand the E symmetry species (+ - +)H (+ - +)D combinations determined in this work are not the same as those reported previously. The carbon mean di pole moment derivative values vary linearly with the average electrone gativities of the terminal atoms, whereas the hydrogen and halogen mea n derivatives are linearly dependent on their own electronegativity va lues.