Ion scattering spectrometry (ISS) with time of flight (TOF) analysis is employed to measure the ion fraction of positively charged hydrogen (H+) projectiles scattered from a well characterized highly oriented pyrolitc graphite (HOPG) surface at a 45 degrees scattering angle, various ingoing/outgoing 14 angles and two different incoming energies (4 and 5 keV). In the theoretical approach, the negative ionization probability is calculated by employing a Green's function formalism to solve the dynamic collisional process. Both theoretical and experimental results are analyzed and contrasted. The theoretical negative ion fraction evolution during the collisional process is described in detail. (C) 2007 Elsevier B.V. All rights reserved.