Changing Vibration Coupling Strengths of Liquid Acetonitrile with an Angle-Tuned Etalon

This work is the first report on
nonzero molecular vibration–vibration
coupling in an infrared cavity–vibration experiment. Vibration–vibration
coupling strength is determined as a cavity mode of parallel spaced
mirrors (etalon mode or fringe) is angle-tuned in the region between
two vibrations of liquid acetonitrile which are Fermi coupled, namely,
a CN stretch dominated vibration and a nearby combination band dominated
by the symmetric CH3 bend and C–C stretch. All other
infrared cavity–vibration work to date involving more than
one vibration has used a value of zero for vibration–vibration
coupling; however, this work starts with Fermi coupled vibrations
and reveals that there are changes in the vibration–vibration
coupling and cavity–vibration couplings as the cavity mode
is angle-tuned between the interacting vibrations. The ability to
change fundamental vibrational dynamics within a cavity is an exciting
result which helps to build a foundation for understanding molecular
vibrational dynamics in parallel plate etalon cavities.