Relation Between Bond Angle and Carbon-Oxygen Stretching Frequencies in CO 2 -Containing Compounds.

The symmetric (ν _s ) and antisymmetric (ν _as ) O-C-O stretching modes of CO ₂ -containing compounds encode structural information that can be difficult to decipher, due to the sensitivity of these spectral features to small shifts in charge distribution and structure, as well as the anharmonicities of these two vibrational modes. In this work, we discuss the relation between the frequency of these modes and the geometry of the O-C-O group, showing that the splitting between ν _s and ν _as (Δν _as-s = ν _as - ν _s ) can be predicted based only on the O-C-O bond angle obtained from quantum chemical calculations with reasonable accuracy (±46 cm ^-1 , R ² = 0.994). The relationship is shown to hold for the infrared spectra of a variety of CO ₂ -containing molecules measured in vacuo. The origins of this model are discussed in the framework of elementary mode analysis.