The enthalpies of formation of AsXn molecules, where X = H, F or Cl, and n = 1, 2 or 3, by RCCSD(T) and UCCSD(T)-F12x calculations

Abstract

RCCSD(T) and UCCSD(T)-F12x calculations were performed on AsX_n molecules, where X = H, F or Cl, and n = 1, 2 or 3, and related species, in order to evaluate their enthalpies of formation (ΔH_f^Ø). The recommended ΔH_f^Ø values obtained from the present investigation are AsH, 57.7(2); AsF, −7.9(3); AsCl, 27.2(4); AsH₂, 39.8(4); AsF₂, −96.6(9); AsCl₂, −17.8(10); AsH₃, 17.1(4); AsF₃ −196.0(5) and AsCl₃, −59.1(27) kcal mole⁻¹. These values are anchored only on one thermodynamic quantity, namely, ΔH_f^Ø(As) (= 70.3 kcal mole⁻¹). In the calculations, the fully-relativistic small-core effective core potential (ECP10MDF) was used for As. Contributions from outer core correlation of As 3d¹⁰ electrons were computed explicitly in both RCCSD(T) and UCCSD(T)-F12 calculations with additional tight basis functions designed for As 3d¹⁰ electrons. Basis sets of up to augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality were used in RCCSD(T) calculations and computed relative electronic energies were extrapolated to the complete basis set (CBS) limit. For the simplified, explicitly correlated UCCSD(T)-F12x calculations, basis sets of up to quadruple-zeta (QZ) quality were employed. Based on the RCCSD(T)/CBS benchmark values, the reliability of available theoretical and experimental values have been assessed.