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

A computational study of the [Ar,O,H](+) cation, a possible interference io n in ICP mass spectrometry, has been performed. Three singlets and three tr iplets at local minima were found. Structural optimizations were performed at MP2(full)/aug-cc-pVTZ and single-point calculations were done at these o ptimum 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. Tw o 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 kca l 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), res pectively. 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), re spectively.