Collisional activation of the endoergic hydrogen atom transfer reaction S−(2P)+H2→SH−+H

Abstract

Guided ion beam tandem mass spectrometry and ab initio calculations are used to investigate the reactions of S−(2P) with H2 and D2. 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∞v collinear reaction path. The threshold energy yields the bond dissociation energy D0(S−−H)=373.1 ± 4.3 kJ/mol. Using literature values for electron affinities, we derive D0(S–H)=350.0±4.3 kJ/mol, in agreement with previous values. We also obtain gas phase acidities for H2S and SH, ΔacidH298(H2S)=1467.9±4.3 kJ/mol and ΔacidH298(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−+H2 reactants.