Herein, we studied how FeCp2 can decompose in an Ar plasma at medium vacuum conditions, as used in the e-CVD process. We studied the decomposition using in-situ optical emission spectroscopy (OES) and in-situ quadrupole mass spectrometer (QMS), combined with in-silico studies, using density functional theory (DFT) to calculate the reaction energies. The focus in this paper is the FeCp2 plasma decomposition, based on observations by OES and QMS along with DFT calculations on the thermodynamics of the reactions. Studying the kinetics and cross sections is not within the scope of this paper. From our results we propose plasma chemical decomposition mechanisms of ferrocene where the Cp ligands are broken off and decomposes to small hydrocarbon fragments.