The development of a numerical code for the modeling of negative ion sources requires the knowledge of a lot of processes occurring both in the gas phase and at the surface. The present work concerns the effect of surface processes (in particular atomic wall recombination) on the kinetics of production/destruction of negative ions. Especially in the pressure regimes useful to produce negative hydrogen ions for thermonuclear applications, wall processes can strongly affect the negative ion production acting on the vibrational distribution of molecular hydrogen.