The C-s and C-2v paths of the Al-2((3)Pi(u;)(1)Sigma(g)(+)) + H-2 reaction to form the singlet dibridged Al(mu-H)(2)Al product, detected repeatedly in solid matrices, has been investigated. The performance of a number of high level single-reference and CASSCF based ab initio and DFT methods are compared. The key finding is that the two singlet routes involve no energetic barrier for the H-H bond breakage relative to the singlet reactants. The theoretical results are in accord with the recent experimental observation that Al-2 dimer reacted spontaneously with H-2 in solid matrix. (C) 2004 Elsevier B.V. All rights reserved.