THE DIPOLE GRADIENT FOR ISOLATED C-H STRETCHES .2. PARTIALLY DEUTERATED METHYL-FLUORIDE, METHYL-CHLORIDE AND METHYL-IODIDE

The vapour phase infrared contours, at 0.5 cm-1 resolution, of the C-H stretch fundamental in CHD2F, CHD2Cl and CHD2I have been simulated using anharmonic rigid asymmetric top calculations. The smallest angle between the C-H bond direction and the dipole gradient that reproduces the experimental contour, obtained by rotating the gradient from the C-H bond towards the bisector of the methyl group, was found to be 15 +/- 5-degrees in CHD2F, 38 +/- 2-degrees in CHD2Cl and 49 +/- 3-degrees in CHD2I. Together with the corresponding value for CHD2Br, these results are compared with the polarizability of the halogen atom.