Appendix E FTIR Frequency scale calibration
Effect of IR beam restricting accessories on frequency
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the expected frequency for the NIR water vapor line when measured with an open
beam or large throughput sampling accessory.
Effect of IR beam restricting accessories on frequency
A common example of a beam restricting accessory is the vial sampling accessory used
with the MB3600. In order to achieve a uniform optical path through the curved walls of
small glass vials, the IR beam is restricted by means of a 1mm wide vertical slit in the vial
sampling accessory. This changes the illumination distribution and hence the frequency
Figure E- 2. Illumination distribution as a function of frequency shift for figure 1 distribution
