Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized from CH4/N2, C2H4/N2, and C2H2/N2 gas mixtures using inductively coupled rf plasmas. These deposition systems were characterized by means of optical emission spectroscopy and mass spectrometry (MS). The effects of varying the nitrogen partial pressure on film growth and film properties were investigated, and experimental results indicate that the hydrocarbon species produced in the gas phase contribute directly to film growth. Although the CN radical is formed in the mixed gas systems, it does not appear to be a factor in controlling the rate of film deposition. The nature and energy of the ions in these systems were explored with MS. No clear dependence of ion energy on mass or plasma conditions was observed. Although films formed in the methane and ethylene systems were relatively smooth, a-C:N:H films prepared from acetylene-nitrogen plasmas had comparatively rough surfaces, most likely as a result of the strong gas-phase polymerization process produced by the ion-molecule reactions, CnHy++C2H2→C(n+2)Hy++H2 (n≫1, y=1–3). Correlations between the a-C:N:H growth processes and the gas-phase plasma diagnostic data are d- iscussed.