We report on the synthesis of carbon nitride thin films using ArF excimer laser (lambda = 193 nm) irradiation of acetylene and ammonia gaseous mixtures. The influence of the precursor composition on the nitrogen incorporation in the films was investigated by different techniques, namely X-ray photoelectron spectrometry (XPS), low-energy electron induced X-ray spectrometry (LEEIXS) and IR spectrometry. Scanning electron microscopy was used to characterise the microstructure of the deposited films. As shown by XPS the N/C atomic ratio varies by changing the precursor composition and reaches a maximum of 0.75 for a flow rate ratio NH3:C2H2 = 5:1. Nitrogen as revealed by Fourier transform infrared spectrometry (FTIR) is single or double chemically bonded to carbon. The morphology of the deposited films investigated by scanning electron microscopy (SEM) depends also on the deposition parameters.