By performing quantum dynamics calculations on ab initio potential energy surfaces (PESs), we investigate and discuss the effects of the initial kinetic and vibrational energies and the orientation of the incident hydrogen molecule (H-2) on the dissociative adsorption dynamics Of H2 On a Pt(111) surface. Using the coupled channel method, we calculate the sticking probabilities for H-2 in the kinetic energy range E-t = 0.01-1.2 eV and initially in the vibrational ground state and in the first two excited states. Our results indicate that the sticking probability plots for H2 show very weak or no vibrationally assisted sticking (VAS) effect in the various configurations we considered. This is attributed to the early barrier position along the path of minimum potential with respect to the onset of hydrogen dissociation. Compared to other surfaces we studied, this behavior is similar to the cases of the dissociative adsorption of H-2 on the surfaces of Ti(0001) and La(0001), and to the armchair and zigzag edges of graphite. (c) 2005 Elsevier B.V All rights reserved.