[en] A physical/chemical model is presented for the reaction kinetics for methane formation from carbon, due to bombardment by energetic (∼ 100's eV) H⁺ ions and thermal (∼ 1 eV) H⁰ atoms. While the model was developed for H⁺ and H⁰, it can be readily applied to non-hydrogenic energetic particles (ions or atoms, e.g., Ar⁺, He⁺, He) in combination with thermal (∼ 1 eV) hydrogen (again ions or atoms) impacting on carbon. Both collisional (in the case of the energetic particles) and chemical reaction processes are included. Special cases of sub-eV H⁰ alone, energetic H⁺ alone and combined H⁰ plus H⁺ were considered and fitted to experimental data. Generally good agreement was found between theoretical predictions and experimental results over the experimental flux and H⁺ energy ranges studied (H⁰ flux: 6x10¹⁴ - 7x10¹⁵ H⁰/cm²s, H⁺ flux: 6x10¹² - 5x10¹⁵ H⁺/cm²s, H⁺ energy: 300 eV/H⁺ and 1 keV/H⁺)