Here is a link to the experiment I make reference to in the question:
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_example.html

And here are some animations and explanations of the different ways in which molecules react with electromagnetic radiation:

http://hyperphysics.phy-astr.gsu.edu/hbase/mod3.html

http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html