Thermonicolet Omnic Software User's Guide 6.1 (PDF) - Charles E ...

4. Collect a sample spectrum with no sample in place using Collect Sample
in the Collect menu.
Since the sample spectrum contains water and carbon dioxide peaks, it can be
used only to correct spectra for both water and carbon dioxide. To use this
spectrum as a reference, specify it as both the water and carbon dioxide
references in the Process options, and set Correction to H2O And CO2 in the
Experiment Setup dialog box (see “Selecting a correction type” in the
“Collect” chapter).
Specifying an
additional reference for
atmospheric suppression
If you find that the Automatic Atmospheric Suppression option on the Collect tab
of the Experiment Setup dialog box does not adequately suppress the effects of
water vapor and carbon dioxide absorptions in the sample spectra you collect, you
can use the features in the Atmospheric Suppression box to improve your results.
The Automatic Atmospheric Suppression option uses a quantitative model to
suppress water and carbon dioxide effects. You can improve this model by
collecting your own reference spectrum and including it when the model is
generated.
When you collect the spectrum, use the following parameter settings in the
Experiment Setup dialog box:
• Set Resolution to 0.5 on the Collect tab. If the highest resolution (smallest
numerical setting) available for your spectrometer is 1 wavenumber, use that
setting instead.
• Set Final Format to Interferogram on the Collect tab.
• Turn on Save Interferograms on the Collect tab.
Collect your reference spectrum without a sample installed, under the same
environmental conditions as will exist when you later collect your sample spectra.
Save the spectrum and then use the Browse button in the Atmospheric
Suppression box on the Process tab to locate and select the spectrum. After you
select the spectrum and choose Open, its pathname appears in the Atmospheric
Suppression box. To include this spectrum when the model is calculated, choose
Add. You can repeat this process (using the Browse button and then the Add
button) to include more than one additional reference spectrum in the model. The
next time you collect a spectrum with Automatic Atmospheric Suppression turned
on, the model will be used.
If you want all of the currently stored models recalculated using the reference
spectrum, choose Update. The calculations can take a long time if you have a
number of models.
Note
The first time you use the new model, data collection will be delayed while the
method is recalibrated. ▲
Window options
The Window options appear when you click the Windows tab.
94 Thermo Nicolet