Infrared (IR) absorption spectroscopy and mass spectrometry have been simultaneously applied to dusty radiofrequency (RF) plasmas in methane, acetylene and ethylene. The combination of IR absorption spectroscopy and mass spectrometry allows the chemical composition and structure of the most relevant plasma-produced neutral species, the ionic plasma composition and the chemical composition of the nanometer-sized particles to be precisely identified. The production of acetylenic compounds (C2Hx) seems to be a key mechanism for the powder formation in all the investigated hydrocarbon plasmas. Electron attachment to acetylenic compounds and the following ion-neutral reactions might lead to the high-mass carbon anions, which are trapped in the plasma and finally end in powder formation. The hydrogenation of the monomer strongly influences the composition of the ions. Finally the composition of the plasma-produced particles is mainly sp(3) bonded carbon and the infrared spectra show similarities to that of polyethylene.