A Fourier Transform Infrared (FTIR) Spectrometer uses the technique of Michelson interferometry. A beam of radiation from the source, S, is focused on a beam splitter constructed such that half the beam is reflected to a fixed mirror. The other half of the beam is transmitted to a moving mirror which reflects the beam back to the beam splitter from where it travels, recombined with the original half beam, to the detector, D.
The IR intensity variation
with optical path difference (interferogram) is the Fourier transform
of the (broadband) incident radiation. The IR absorption spectrum can
be obtained by measuring an interferogram with and without a sample in
the beam and transforming the interferograms into spectra.
in our Laboratory
FTIR can be used as a powerful
tool for investigating molecular conformation and the hindered rotation
of lateral groups around the molecular long axis in chiral SmC liquid
crystals. With polarized incident radiation, the IR spectrum yields orientational
information about selected chemical groups.
We are currently investigating
the rotational hindrance of carbonyl and chiral groups by measuring the
IR absorption spectra of various FLC materials as a function of incident
polarization and the sign of the applied electric field. The resultant
spectra allow us to calculate the orientational distribution of lateral
groups around the molecular long axis. An example showing hindered rotation
of the carbonyl group is illustrated in Fig.2.
We are also studying the switching dynamics of selected functional groups using time-resolved FTIR with nanosecond resolution.
For more information on this project, contact Noel Clark.