The first ionization energy has been shown to be somewhere between 6.6 and 7.2 eV (637 -695 kJ/mol), as shown in previous studies by Ryan et al., and Bär et al., and is therefore in line with our calculated value of 7 eV. The ionization cross section of FeCp2 has previously been estimated to 3.8 * 10 -15 cm 2 , 43 while the ionization cross section to achieve FeCp2 2+ (reaction 7) has not been found. Since the first ionization potential of FeCp2 (7 eV) is lower than that of Ar (15.76 eV) and that N II excitation at 336.7 nm (11.0 eV, Fig. ) was observed and that the electron impact ionization cross section has been obtained, we still assume that reaction 6 will occur, albeit not being a dominant reaction. The second ionization potential to obtain FeCp2 2+ is 4.6 eV higher than the one of FeCp2 + , indicating that FeCp2 2+ is likely not a dominant species in the e-CVD plasma. Therefore, additional reactions including FeCp2 2+ decomposition can be seen in Table in supplementary material.