An hybrid functional which includes a larger amount of pure exchange has been specially designed for the description of hydrogen-only systems. Both the H abstraction by H-2 and the H-2n+1(+) clusters have been investigated. Comparison with experimental values shows that the proposed functional gives dissociation energies and vibrational frequencies better than previous ab initio calculations. The results compare favorably with those obtained by a coupled clusters method [CCSD(T)], also performed in this work for sake of reference data. (C) 1997 American Institute of Physics.