Another advantage of the IRRAS method is also apparent from figure 3 as compared
to figure 1, namely that the whole mid infra red region is measured as compared
to the ATR – IR method, which has the blind region mentioned earlier. The two
peaks around 1785 cm-1 and 2500 cm-1 seen in figure 3 could not be detected in
the spectra shown in figure 1 and 2. The other chemical peaks from the ATR – IR
measurement around 3000 cm-1, around 1500 cm-1 and around 1000 cm-1 seen in
figure 1 are also found in figure 3. At closecomparison one can see that these peaks
are shifted to higher wavenumbers in the IRRAS spectra as compared to the ATR –
IR spectra. This difference is most likely due to the fact that the sample is pressed
against the ATR – IR crystal in the ATR –IR experiment. It is a well known effect of
the ATR – IR method that the peaks shift as a function of the applied pressure.