Gaseous samples seeded in helium or other carrier gas mixtures are introduced into the Teflon-coated reservoir and expanded into the vacuum chamber through a narrow (0.2 mm) but extremely long (600 mm) slit nozzle (fine - but lengthy). This nozzle length enables recording of FTIR spectra with highest sensitivity.
The FTIR spectrometer (Bruker IFS 66v/S) is synchronized to gas pulses with durations of few tenths of a second. Waiting times between pulses on the order of 15 to 120 s ensure a sufficiently low background pressure of max. 1 mbar during expansions. The spectrometer can be equipped with CaF2, KBr, CsI or Mylar optics. A 150 W tungsten lamp or Globar rod are used as light sources, according to the desired spectral range. Detectors can also be varied from InGaAs and InSb elements for near-IR measurements, an HgCdTe detector for mid-IR spectra to a liquid-helium cooled Si-bolometer in the far-IR spectral region. Different combinations of these elements allow to carry out FTIR measurements from the far (200 cm-1) to the near (8000 cm-1) infrared .