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log reflectance vs absorbance in Bruker OPUS software and particle size in DRIFTS

kristian's picture

Dear all,
I am new to diffuse reflectance and am having some trouble understanding the Bruker software OPUS 7.5.
1.  For the measurement, in the menu "Result spectrum", one can choose  between various options, including Log Reflectance, Reflectance, Transmittance, Absorbance, Kubelka Munk etc.
I have been recommended to measure in Log Reflectance since it is the original data, but I want to plot my data in absorbance. The software offers the possibility of converting between the various options, but the conversion LogReflectance -> Absorbance is not available.
Am I to understand that "Log Reflectance" in OPUS is log(1/R) and equivalent to absorbance? Or is it log (R)? And is there a reason why that conversion option is not available, as in it can't be done?
2. My second question is about particle size in DRIFTS. I have read somewhere that particles must be sieved to below 5 um. But since this is too small for the mesh size of the grid supporting my particles, I am working with about 180 um. Does anyone have any good reference explaining the effect of particle size, or at least can tell me if 180 um is ok?