On the symmetry groups of non-rigid molecules

Abstract

A counter-example is produced to show that Altmann's representation of the group S of a non-rigid molecule as a semi-direct product of an ‘isodynamic’ group I and a point group G in the form S = I ^ G does not always hold in the Longuet-Higgins classification scheme. Altmann's proof of this relation requires reconsideration. However, the discrepancies between the two treatments in the case of boron trimethyl are due to Altmann's use of an operation of questionable validity called a ‘flip’, denoted by Z ₂ ^I.