Quite obviously those vibrations of this molecule that have vectors predominantly along the chain will interact best with resonant infrared radiation polarised vertically. In a polymer there is almost always only one preferred direction - the stretch direction i.e. the chain axis. Coke bottles are just such a case. The PET sheet forming the walls deforms in 2 directions and hence the benzene rings lie roughly parallel to the wall surfaces. There are many other examples of oriented materials from minerals to fibres, films, some coatings, liquid crystals etc, etc.
Orientation can even be present and be an unwanted nuisance.
In all these cases infrared can be pressed into service. The principle is to introduce a polariser into the optical system and study the spectrum with the sample oriented in different ways with respect to the polariser. In the case of a film or fibre two measurements are obvious. If 3 way orientation is to be monitored a third measurement can be made. If the sample is PET the out of plane CH deformations of the arometic rings will lie along the axis.