Guided ion beam tandem mass spectrometry and ab initio calculations are used to investigate the reactions of S-(P-2) with H-2 and D-2. The hydrogen atom transfer reaction to form SH- or SD- is observed at collision energies above the reaction endoergicity. Coupled-cluster theory calculations indicate that the hydrogen abstraction reaction occurs with no barrier along the C-infinity v collinear reaction path. The threshold energy yields the bond dissociation energy D-0(S--H) = 373.1 +/- 4.3 kJ/mol. Using literature values for electron affinities, we derive D-0(S-H) = 350.0 +/- 4.3 kJ/mol, in agreement with previous values. We also obtain gas phase acidities for H2S and SH, Delta(acid)H(298)(H2S) = 1467.9 +/- 4.3 kJ/mol and Delta(acid)H(298)(SH) = 1465.2 +/- 4.3 kJ/mol. The competition between hydrogen atom transfer and the exoergic associative detachment reaction forming SH2+e(-) is discussed. Calculations reveal that the transition state for insertion leading to associative detachment is a bent asymmetric SHH- species with an energy of 47 kJ/mol relative to S- + H-2 reactants. (C) 2000 American Institute of Physics. [S0021-9606(00)02110-3].