Water-catalysis in the gas phase reaction of dithioformic acid with hydroxyl radical: global reaction route mapping of oxidative pathways for hydrogen abstraction

Abstract

The catalytic-role of water in the gas phase oxidation reaction of hydroxyl radical with dithioformic acid (DTFA) has been investigated through quantum mechanical computations performed using MP2, CCSD(T) and DFT methods. The pre-reaction complexes, which can considerably influence the thermodynamics and kinetics, are systematically explored through a global reaction route mapping (GRRM) method. The computations successfully revealed a positive catalytic role of water which is observed to stabilize the pre-reaction complexes as well as respective transition states, resulting in a significant lowering of the potential energy surface. The standard Gibbs free energy change for the explored pathways was also analyzed. The abstraction of acidic-hydrogen in DTFA was found to be both thermodynamically and kinetically more feasible than the formyl-hydrogen abstraction both in the presence and absence of water. Notably, a few of the pathways are observed to proceed through a proton-coupled electron-transfer mechanism. However, only formyl-hydrogen abstraction in the presence of water could be traced by all the different theoretical methods employed in this work.