Vibrational description of the stretching modes of octahedral molecules: a local-to-normal mode transition criterion

Abstract

A criterion to establish the normal-to-local mode transition in the series of octahedral molecules SF, WF and UF in terms of the suitability to estimate force constants in a local mode model is proposed. The analysis is accomplished by considering the stretching degrees of freedom in a polyad-conserving model where two types of local neighbour interactions are involved. The connection between the local and normal mode schemes leads to establish a quantitative locality degree involving both force and structure constants, providing the expected normal (SF) → local (UF) trend. This approach allows reliable force constants to be estimated in the framework of a polyad-conserving local scheme.