This paper presents the results on a study the processes of physicochemical interactions of water with graphite. The main regularities of the formation of H-2, HD and D-2 molecules on the graphite surface were determined. It was shown that the fraction of D-2 and HD in the gaseous outcome increases in the process of heating, and the quasi-equilibrium state of the graphite's absorption of hydrogen isotopes at the initial stages of interaction is significant: the flow of dissolved atoms into the sample volume is higher than the desorption flow. We suppose that this is due to the higher rate of dissolution of hydrogen atoms in the volume of graphite. We also estimated also the separation factor for the graphite surface-volume system for hydrogen atoms, which was 1.53 for the selected experimental conditions. The temperature dependence of the effective rate constant K-s for the formation of hydrogen isotope molecules in the interaction of graphite with water vapour in the range of 1100 degrees C-1200 degrees C was determined. It turned out that K-s(D-2) > K-s(HD) > K-s(H-2). (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.