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The paper presents the results of the combined investigation of changes in the carbon nanotubes structure caused by hydrogenation. Hydrogen adsorption by bundles of single-wall carbon nanotubes (SWNTs) was simulated by the molecular mechanics and DFT-LDA methods and applied to interpret the results of the experimental study carried out by using high-resolution X-ray absorption and photoelectron spectroscopy. As a result, new aspects of physical and chemical adsorption of hydrogen atoms on SWNTs were revealed, as well as preferable ways for SWNTs hydrogenation. Due to van-der-Waals interactions, location of hydrogen molecules inside the channels is energetically more favorable than that outside the channels. Chemical covalent bonds between hydrogen atoms and nanotube walls arise with formation of the C 4 H and C 2 H phases. However, not the entire surface of the SWNTs located inside the bundles is accessible for hydrogenation but only segments adjacent to triangular pores. Image 1 • SWNTs structure changes caused by hydrogenation were elucidated. • Covalent bonds between H atoms and SWNT arise with formation of C 4 H and C 2 H phases. • Hydrogen was shown to be able to penetrate into the triangular intertube channels. • Location of H molecules inside the CNT channels is energetically more favorable. • SWNT segments adjacent to triangular pores are only accessible for hydrogenation. [ABSTRACT FROM AUTHOR]