Charge exchange in a large-angle single collision was studied for medium energy He+ impact on NiSi2(1 1 1), MgO(0 0 1), KI(0 0 1) and Si(1 1 1)-root3- root3-Sb and for Ne+ impact on NiSi2(1 1 1) using a toroidal electrostatic analyzer with an excellent energy resolution (DeltaE/E) of 9 x 10(-4). We measured charge state distributions (CSDs) for He ions backscattered from the top-layer atoms of single crystals under channeling and blocking geometries. It was found that the CSDs were not equilibrated for He ions scattered from low Z atoms and the lower the target Z number, the larger the average charge. The path-length to attain a charge state equilibrium is very short, in a few mono-layer range and thus it yields surface peaks in backscattering spectra even from amorphous solids which were measured with an electrostatic or magnetic spectrometer. In the case of Ne+ impact on Ni atoms of NiSi2(111), the CSDs are also not equilibrated and the average charge is gradually decreased with increase in Ne velocity in the velocity range from 0.4 to 0.8 x 10(8) cm/s. The CSDs are strongly dependent on exit angle with respect to surface plane. We propose a simple model to explain qualitatively the charge exchange process in a large-angle collision at solid surfaces. (C) 2002 Elsevier Science B.V. All rights reserved.