Amorphous carbon and hydrogen containing amorphous carbon films have been prepared by evaporating polycrystalline graphite in hydrogen-free atmosphere (p(H2) < 10(-8) mbar) and in the presence of hydrogen at different pressures (3 x 10(-4) -1.7 x 10(-2) mbar), respectively. After deposition, the films have been characterized by in situ photoelectron spectroscopy. The composition of the gas phase during graphite evaporation in the presence of hydrogen was measured with a quadrupole mass spectrometer. The gas phase data have been correlated to the hydrogen content in the film. It is found that hydrogen is incorporated preferably into amorphous carbon when already bound to carbon in the form of CH(x) (x = 1,2,3) in the gas phase. In addition, the bombardment of a growing amorphous carbon film with high energy hydrogen ions has turned out to be a quite effective means of incorporating hydrogen into a-C.