CH4[sbnd]O2, NH3[sbnd]O2, H2O[sbnd]O2 and HF[sbnd]O2 triplet complexes. Ab initio studies and comparisons. From van der Waals to hydrogen bonding

Abstract

Using coupled cluster singles, doubles and perturbative triples CCSD(T) methods with augmented correlation consistent basis sets up to the 5Z level, dissociation energies and structural parameters were obtained for CH4O2, NH3O2, H2OO2 and HFO2 triplet complexes. Most stable for CH4O2 is a structure with three hydrogens facing O2 in T-shape (dissociation energy De = 168 cm−1), for NH3O2 a structure with two hydrogens facing O2 in X shape (De = 196 cm−1), and for H2OO2 (De = 222 cm−1) and HFO2 (De = 301 cm−1) a hydrogen bonded structure. Energies, geometries, vibrational frequencies, infrared intensities and dipole/quadrupole moments of the four complexes were compared. While such properties change gradually from CH4O2 to H2OO2, they are much more pronounced for HFO2. The transition from van der Waals to hydrogen bonding was followed. There are significant changes in the O2 frequencies for hydrogen-bonded structures. Due to increased vibrational intensities such complexes may contribute to the greenhouse effect.