The fragmentation pattern of FeCp2 in the electron ionizer (EI), i.e., without a plasma discharge, is shown in Fig. , indicating peaks at a m/z of By temporally resolving the measurement, i.e., separating the precursor supply and the plasma discharge in time, the signals originating from EI ionization of FeCp2 in the QMS can be distinguished from those by plasma decomposition using the MID sampling mode, and thereby detecting a few pre-selected m/z signals as a function of time. The detection of C2 and CH by OES (Fig. ) suggests that acetylene, C2H2, m/z = 26, could form in the decomposition of the Cp ligands, which has also been reported in femtosecond laser decomposition of FeCp2. Linear and cyclic C3H3 • , m/z = 39, was also suggested to be a by-product in reaction 2 and has earlier been proposed to be a by-product in microplasma decomposition of ferrocene. We therefore studied the temporal trends of m/z = 26 and m/z = 39 (Fig. and Fig. , respectively). The C2H2 + signal spikes as the plasma is ignited and returns to the baseline when the plasma is turned off, which can also be seen for m/z = 39 (C3H3 + ). From these observations, it is likely that the Cp ligand decomposes to C2H2 and C3H3 in the plasma volume, according to reaction 2, strengthening our discussion of our OES results above. We also note that m/z = 30 (Fig. ), corresponding to C2H6 + , showed the same trend as for C2H2 + and C3H3 + , although with a higher detected signal. The higher signal of C2H6 + can be explained by the saturation of the C≡C-bond of C2H2 + , according to reaction 3, having a reaction enthalpy of -321.1 kJ/mol (-3.3 eV), see Table . The white areas correspond to both precursor and plasma off, i.e., purging the chamber, the grey areas correspond to precursor on and plasma off, i.e., a pulse of ferrocene, and the pink areas correspond to precursor off and plasma on, i.e., a plasma pulse. Note the partial pressure differences in the y-axis.