Experimental - Spectroscopy

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June 2011 Spectroscopy 26(6) 25
(a)
Transmittance
1
0.8
0.6
0.4
0.2
(b) 0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Transmittance
0
-0.2
4000 5000 6000 7000 8000 9000 10,000
Wavelength
0.1
0
-0.1
4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000
Wavelength
(c) 0.1
0.9
(d)
1
0.95
Transmittance
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Transmittance
0.9
0.85
0.8
0.75
0.7
0.65
5000 5500 6000 6500
Wavelength
(e) 1
6500 6600 6700 6800 6900 7000 7100 7200 7300 7400 7500
Wavelength
0.95
0.9
Transmittance
0.85
0.8
0.75
0.7
0.65
7500 8000 8500 9000
Wavelength
Figure 3: Transmission spectra of mixtures of dichloromethane and n-heptane: (a) 4000 to 10,000 cm -1 ; (b) 4000–5000 cm -1 ; (c) 5000–6500 cm -1 ;
(d) 6500–7500 cm -1 ; (e) 7600–9000 cm -1 .
in the previous presentations of the
spectra because the other spectra in
the set obscure the isosbestic points.
Examining the spectra of the
two-component mixtures, however,
reveals a plethora of isosbestic points.
In fact, when we look at the expansions
of the wavelength ranges, we
find that all three sets of two-component
mixtures contain multiple
isosbestic points.
Another phenomenon more easily
seen in the spectra of the twocomponent
mixtures is the presence
of the expected nonlinearity of the
transmission spectra with respect
to composition, especially for the
stronger absorbance bands. Because
the strongest absorbance bands in
the spectra generally fall in the range
of 5000–6500 cm -1 , this nonlinearity
is very visible in the bands of the
two-component mixtures falling in
this range. Examples where this ef-