PMFTIR procedure for Vector 22 setup (C-H stretch measurements)

 

Start-up

 

1. Fill liquid nitrogen into the InSb detector before switch on the small black control box.

 

2. On starting opus program from windows start menu.

 

Operator name:           pmftir ch

Password:                   corn

 

3. Go to Measure, Measurement and Basic tab and load experiment PMFTIR CH.XPM.

 

4. Go to Check signal tab and confirm that an interferogram is visible. If not, reload expt and check again (assuming detector is cooled and on etc). On the smaller TDS 210 oscilloscope the interferogram can also be observed.

 

5. Check the amplitude of the sample sinusoidal signal on the Tek 2445 scope.

 

Ensure that the sample signal amplitude is around 0.5 2.0 V. At higher voltages (2-3 V) some peak distortion and non-linearity effects can be observed. Also take care not to adjust settings when comparing different samples, as there is a change in the peak amplitude depending on the input signal amplitude over most of the voltage range. Alternatively turn GWC box to an output gain of 2 but peak definition is poorer with respect to background.

 

Take measurements

 

6. For a single block use manual measurements.

           

Switch the GWC box to LOCAL and SUM. Go to Measure, Measurement and Basic tab, and collect Background (10 scans). Then switch to DIFF and collect Sample (50 scans). The spectrum will be displayed automatically.

 

7. For multiple blocks using macro.

 

Switch GWC box to EXT.

            Exit Measure, Measurement window (if open).

 

Click the FTIR CH icon in the toolbar to start the macro. On starting macro a dialog window will appear where you can choose storage name and file path (all personal folders are in drive D). Note that a copy of the averaged file (in opus format, not ascii) will also be dumped in c:/opus_nt/pmftir/average.

 

Each scan is displayed on the screen. After the chosen number of blocks an average dialog window appears. Drag the TR graph icon of the first spectrum into the top first window. Secondly select the TR graph icon of the second file and while holding shift select the TR graph icon of the last spectrum and drag all the spectra into the lower average window and click continue.

 

On finishing scan, to avoid confusion delete all the individual run spectra by clicking on the blue page icon next to the file, use the shift key to select all the desired files and then right click mouse and select unload files, press continue to delete all.

 

 

PM-modulator

 

Phase retardation = 0.5, Wavelength = 3.2 mm.

 

The amplitude setting should be that the peaks of interests are resting at the top of the PEM response curve.

 

GWC demodulation box

 

The phase adjustment should be such that the peak of the sinusoidal response from the sample observed on the scope is aligned with downwards edge of the square TTL pulse.

 

INPUT GAIN = 10

OUTPUT GAIN = 5

 

NB if the amplitude of the sinusoidal signal from the InSb detector is too high (> ~ 3V) then the output gain has to be reduced to 2 or close iris to reduce signal to 0.5-1.5 V).

 

FTIR

 

The cutoff point for the InSb detector is about 1800 cm-1 therefore scan from 1870 to 4000 cm-1.