Getting Started with Spectrum Software . 89
Atmospheric (CO
2
/H
2
O) Suppression
Atmospheric suppression, selected by default on the Setup Instrument Advanced tab
(Figure 77), is an atmospheric correction routine.
Figure 79 Setup Instrument Advanced tab in Spectrum
This routine is more powerful than simple subtraction, overcoming the following issues:
• Non-linearity due to resolution
• The measured spectrum is temperature dependent
• Lineshape and calibration are affected by J-stop and sample or accessory.
When CO2/H2O is switched on, the software uses a single reference spectrum derived from
high-resolution data and our understanding of the instrument to model the lineshape, then
finds the current real instrument parameters by least-squares fitting to the measured
spectrum.
Figure 80 Correction of an MIR spectrum at 4 cm
−1
resolution
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