The isomerisation of H2XY to HXYH (X, Y = O, S, and Se)*

Abstract

Oxywater(HOO) is an intermediate in the oxidation of hydrogen peroxide (HOOH), and along with its relatives HSS and HSeSe, plays an important role in atmospheric and biochemical processes. In this research, we study the isomerisation of HXY species to HXYH (X, Y = O, S, Se) using ab initio methods. Geometries and harmonic frequencies were obtained using both a scalar relativistic X2C-1e-CCSD(T) approach and non-relativistic CCSD(T) using an effective core potential on Se. A focal point approach was used to extrapolate electronic energies at CCSD(T)/aug-cc-pVTZ geometries to a CCSDT(Q)/CBS level of theory. The isomerisation reactions of HXX to HXXH have barriers of 6.6, 20.6, and 14.1 kcal mol and exothermicities of 45.8, 27.2, and 28.3 kcal mol for X=O, S, and Se, respectively. The isomerisation reactions of HOS and HSO to HOSH have barriers of 15.4 and 44.2 kcal mol and exothermicities of 36.2 and 17.7 kcal mol. The isomerisation reactions of HOSe and HSeO to HOSeH have barriers of 10.1 and 36.2 kcal mol and exothermicities of 33.5 and 31.7 kcal mol. The isomerisation reactions of HSSe and HSeS to HSSeH have barriers of 16.2 and 18.1 kcal mol and exothermicities of 23.3 and 32.1 kcal mol.