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Fringe in aqueous solution of d-mannose

IijimaT's picture
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Dear all,
I am studying on near infrared spectra of sugar aqueous solution.
I found a fringe like pattern in limited wavelength range during analysis of 100mM d-mannose aqueous solution spectrum.
 
Measurement settings are below:
MPA(BRUKER OPTICS); using equipped heater
8cm-1, 128scans; quartz cell, 0.3mm pathlength; 3D-printed Nylon-made cell-holder used
35.1-35.3 degree Celsius sample temperature (monitored by thermocouple); 
 
The resultant spectra are in the figure 1 (black; pure water (magnification x1/100 and offset by -0.02),
red; d-mannose 100mM (magnification x1/100 and offset by -0.02),
green; d-mannose 100mM - pure water difference spectrum).
 
100mM d-mannose spectrum minus pure water spectrum indicated in green line shows fringe like pattern only in 1500-1800nm region.
My question is,  whether appearance of this kind of fringe (signal due to multiple reflection within a layer) only in limited region is common thing or not. And what is contributing to make this pattern?
Would you give me an answer if you have one to this question?
 

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