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A Step-Wise Variable Path Far-Infrared Solution Cell for Use in Vacuum
Volume 32, Number 2 (April 1978) Page 250-251
Far-infrared spectroscopy (particularly at resolutions of 2 cm−1 or better) is complicated by the presence of sharp, strong H2O vapor absorption lines. One common technique for reducing the effect of these lines is to use windows to isolate the sample chamber from the rest of the spectrometer. The sample chamber is then flushed vigorously with dry air or nitrogen, while the rest of the spectrometer is either evacuated or continuously flushed, depending on its construction. The lines due to residual H2O are expected to cancel when the reference and sample spectra are compared. With our instrument (a Digilab FTS 16 interferometer, which can be evacuated) we have achieved better cancellation more quickly by removing the windows from the sample compartment. The entire instrument is then evacuated for each sample. The time required for evacuation is quite short (about 5 min) and when many different sample spectra are to be compared to the same reference spectrum (stored in the computer) it is advantageous not to have to worry about changes in flushing rate or time or in the degree of dryness of the air used for flushing. Also, by removing the windows between the sample compartment and the rest of the interferometer, the signal/noise ratio is improved.