Thin films (similar to 100 nm) of hydrogenated amorphous carbon (a-C:H) have been prepared by plasma-enhanced chemical vapour deposition (PECVD). Surface analysis techniques such as elastic recoil detection with an electromagnetic filter (ERD ExB), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have been used to measure the influence of the arrangement of the internal structure on the retention of hydrogen and the desorption of methane and ethylene from the PECVD carbon films under thermal and ion beam treatments. The parameters of deposition have been adjusted in such a way that the chemical hybridization of the carbon atoms could be tailored (mainly sp(2), sp(3) or a mix of the two hybridizations). The thermal desorption behaviour appears to be greatly influenced by the sp(3)/sp(2) hybridization ratio of the carbon films. With increasing ratio, desorption of hydrogen is shifted to higher temperatures, ethylene desorption is decreased and methane desorption is increased. Ion beam induced desorption (IBID) also depends on the hybridization ratio of the carbon deposits. IBID and TDS results can be understood in terms of enhanced hydrogen mobility for lower density (lower sp(3)/sp(2) ratio) films accompanied by hydrogen recapture in films with a significant degree of sp(2) hybridization.