SIGN OF THE DIPOLE-MOMENT DERIVATIVES IN CH3F, CH3CL, CH3BR, CH3I

It is shown in this paper that the principal methods for reducing the indeterminacy of the sign of (δ M/δOi) (isotropic invariance of M, quantum mechanical calculations, determination of (δM/δOi) via high resolution data or the Stark effect) lead, in the case of CH3X (X = F, Cl, Br, I) molecules, to contradictory conclusions. The discrepancies are illustrated and discussed. It is also pointed out that either a revision of the previous results or a calculation of electro-optical parameters on a set of chemically similar molecules including CH3X could possibly lead to a unique determination of the sign. © 1979.