A mixed PVD/PECVD deposition process of DLC films with acetylene precursor and graphite magnetron target was simulated using a 3D Particle-in-Cell Monte-Carlo (PIC-MC) code. The simulation comprises of a carefully chosen, self-contained plasma chemistry scheme involving 18 species and 150 reactions, and a dynamic deposition model that includes ion subplantation and the creation of dangling bonds. Mass spectroscopic measurements of neutrals and ions have been performed at substrate position in order to validate the simulation's predictions. Despite the difficulty in performing reliable mass spectrometry in reactive plasmas and the impossibility of running PIC-MC simulations with powers and time scales comparable to the experiment, we were able to correlate the simulated and experimental densities with varying discharge powers and acetylene contents. We showed that the relative concentrations vary spatially within the chamber due to differences in species' diffusion, energy or creation area (plasma or chamber). The power dependence of the hydrocarbon ion densities was linear with similar slopes and relative concentrations in experiments and simulations. This is an indication that our model could be extrapolated to relevant experimental conditions and give quantitative predictions on densities, fluxes and energies of principal species, which could be used as input for film growth simulations. It can also form the basis for simulation frameworks of deposition processes that involve the decomposition of C2H2 in low-pressure plasmas (below 1 Pa) with complex reactor geometries and electromagnetic fields.