negative absorption peak in FTIR

[physiks2011]

What does it mean if one found negative absorption in uv-vis absorption graph?

[Jano L.]

Hi,
I have heard this explanation:
in IR spectroscopy you have to subtract signal due to water and CO2 and if their densities decrease in the course of experiment, your background which you want to subtract may become stronger than the actual background. Then you get negative peaks.
Jano

[shawl]

Something are exciting over the UV illumination processes.