A Correlation between Molecular Vibrations and Bond-forming Orbitals

Abstract

IN a recent letter, Heath and Linnett¹ suggested for the treatment of molecular vibrations a new force field, the orbital valency force field. This is based more closely on modern ideas of directed valency than is the simple valency force field. We decided to test the orbital valency force field on methane, which is a convenient molecule to use, since all the deuterium-substituted methanes have been studied². The first result obtained was that the original theory failed in this case. In particular, for CH₄ and CD₄, it was found that, to explain the frequencies of the doubly degenerate bending vibrations, a bending constant (kH/r²) of 1·35 × 10⁵ dynes/cm, was required, whereas the triply degenerate bending vibrations needed a constant of 0·86 × 10⁵ dynes/cm. Bending motions which are members of these two degenerate sets are shown in the accompanying drawings.