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

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(X(2)Pi)-N2O complex has been measured for the first time in the 5.3 microm 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 degrees . The vibrationally averaged (2)A'-(2)A'' energy separation is determined to be epsilon = 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 (2)A'' state is more stable than the (2)A' 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 (2)A'' state.