My lab is going to reconstruct in situ FT-IR system. 

It has been used very simple vacuum system like mbar level, It was hard to remove even gas in in-situ FT IR cell.

I remember, Measure physisorption like BET surface area, ASAP 2020 depressurize to around 2mmHg. 

My question is, what is the level of vacuum to remove Physisorption molecules on the surface in insitu FT-IR system?

My lab is doing heterogeneous catalysts, We are not doing like fine surface. 

I just want to do like KBr pellet with catalysts, and doing some Pyridine or CO adsorption technique.