Hi everyone, I wonder if somebody could help me identify a mystery peak that appears in my FTIR data? The problem has been on-going for several years and I've finally decided to get to the bottom of it!
We're generating a low-temperature plasma in air which creates a host of gas phase chemical species that we flush through ~ 30 cm of pipe into our FTIR gas cell. The cell uses KBr windows and has a 10 cm path length. Plasma produces many reactive species but these typically react quickly to form long-lived species such as O3, N2O, and NO2.
When assessing this 'exhaust' gas with FTIR we see the expected peaks in their expected positions. However, we also see an extremely strong peak at 1356 cm-1 which does not look like anything we would expect. It is this peak I am interested in identifying...
Some clarifying information:
- We always take a background prior to plasma generation, the peak does not appear in this background spectra.
- The peak first appears during plasma generation; critically, it remains even after we have flushed the cell.
- The peak must be related to the KBr windows, other window materials show no sign of it.
- We have tried with brand new windows, straight from the sealed pack, the peak immediately appears once plasma species have been in the cell.
- Our only option to remove the peak is to take a second background, after the cell has been flushed following plasma generation.
- A collaborator in a different country reports a similar issue using a similar plasma system, their FTIR system has a different manufacturer than ours, but again they use KBr windows.
I've tried to attached a plot showing the mystery peak, hope it has worked!
If anyone could help shed some light on this annoying issue I'd be most grateful...