Three ab initio potential energy surfaces of B-2(2), (2)A(1) and (2)Sigma states for the Na + I-2 collision system are calculated on the QCISD(T)/LANL2DZ level. Three reaction channels. neutral reaction, chemical ionization and collision ionization, have been obtained based on analyzing the minimum energy reaction paths. The valence potential energy surfaces (2)A(1) and the ionic state B-2(2) are crossed approximately at R-c = 0.508 nm. Na + I-2 --> Na+ + I-2 is an electronic non-adiabatic process. (C) 2002 Published by Elsevier Science B.V.