Infrared Intensities for Degenerate Modes: The observed infrared
intensity of a degenerate mode is the sum of the intensities of
each degenerate component. A paper by Sørensen and Jørgensen
[2] considers the doubly degenerate bending
modes of linear molecules and shows that the overall intensity is the
sum of the two individual components for the representation
of IR intensities, and slightly less than this for the
representation.
Complaints in this paper about the poor quality of ab initio
intensities are largely put to rest in a published comment by Gwaltney and
Bartlett [3].