Structural characterization of the NO(X2Π)–N2O complex with mid-infrared laser absorption spectroscopy and quantum chemical calculations

Abstract

Both positive and negative ions of N3O2 have been observed in various experiments. The neutral N3O2 was predicted to exist either as a weakly bound NO·N2O complex or a covalent molecule. The rovibrational spectrum of the NO(X2Π)–N2O complex has been measured for the first time in the 5.3 µm region using distributed quantum cascade lasers to probe the direct absorption in a slit-jet supersonic expansion. The observed spectrum is analyzed with a semi-rigid asymmetric rotor Hamiltonian for a planar open-shell complex, giving a bent geometry with an a-axis–NO angle of about 21.9°. The vibrationally averaged 2A′–2A″ energy separation is determined to be ε = 144.56(95) cm−1 for the ground state, indicating that the electronic orbital angular momentum is partially quenched upon complexation. Geometry optimizations of the complex restricted to a planar configuration at the RCCSD(T)/aug-cc-pVTZ level of theory show that the 2A″ state is more stable than the 2A′ state by about 110 cm−1 and the N atom of NO points to the central N atom of N2O at the minimum of the 2A″ state.