Ab initio studies on the NO(X2II) − O2(X3 Σg−) van der Waals complexes in the doublet state

Abstract

ABSTRACTUCCSD(T) and CASPT2 geometry optimisations were performed on six different structures of NO–O2 complexes in doublet states, using aug-cc-pVXZ basis sets up to X = 5. MRCI calculations were carried out at optimised UCCSD(T) and CASPT2 geometries. The most stable structure has NO and O2 arranged nearly parallel in the 2A′′ state, with a counterpoise adjusted dissociation energy De of 179 cm−1 (UCCSD(T) results). For the X-shaped 2A′ isomer De = 144 cm−1. C2v structures have De values between 115 and 121 cm−1, whereas linear structures are least stable. The closest and distances are 3.1–3.4 Å. The X-shaped 2A′′ isomer is not stable. The results are discussed and compared with values for other complexes.