A quantum-chemical study of the geometries and electronic structures of ArO and [Ar,O,H]+: proton affinities of singlet and triplet ArO

Abstract

A computational study of the [Ar,O,H]⁺ cation, a possible interference ion in ICP mass spectrometry, has been performed. Three singlets and three triplets at local minima were found. Structural optimizations were performed at MP2(full)/aug-cc-pVTZ and single-point calculations were done at these optimum geometries using CCSD(T)(full)/aug-cc-pVTZ. The lowest-energy isomer is the singlet Ar–O–H⁺ ion 1, isoelectronic with the hypochlorous acid. Two other singlets, Ar––H–O⁺ and H–Ar⁺––O, are higher in energy by 57.5 and 85.7 kcal mol⁻¹, respectively. The low-energy triplets are Ar––H–O⁺ (0.2 kcal mol⁻¹ above 1) and Ar––OH⁺ (2.3 kcal mol⁻¹ above 1). The third triplet, H–Ar⁺––O, is 33.4 kcal mol⁻¹ above 1. The computed proton affinities of ArO in its singlet and triplet states are 174.1 and 129.9 kcal mol⁻¹, respectively. The deprotonation energy of the singlet ArOH⁺1 strongly depends on the change in multiplicity: 174.1 kcal mol⁻¹ forming singlet ArO, and 130.1 kcal mol⁻¹ forming the triplet. Deprotonation energies of the two low-energy triplets Ar––H–O⁺ and Ar––OH⁺ are 129.9 and 127.8 kcal mol⁻¹, respectively.