Rovibrational Spectrum and Structure of the NO(X2Π)–CO2 Open-shell Complex

Abstract The rovibrational spectrum of the NO(X2Π)–CO2 open-shell complex has been measured in the fundamental band region of NO using an infrared laser absorption spectrometer. Geometry optimizations at restricted configurations with a Cs symmetry at the RCCSD(T)/aug-cc-pvtz level of theory predict that this complex has a T-shaped structure at the global minimum on the ground electronic state (2A”), with the N atom of NO pointing to the C atom of CO2. The observed spectrum is analyzed with an effective Hamiltonian for a planar T-shaped open-shell complex. Half of the possible rotational levels are missing due to spin statistics of the two identical 16O nuclei (I = 0) in the CO2 subunit of the complex. The band-origin of the complex is located at 1880.4518(67) cm-1, which is blue-shifted from that of the NO monomer by about 4.48 cm-1. The rotational constants and the quenching parameter of the electronic orbital angular momentum of NO in both ground and excited vibrational states have been determined accurately. The intermolecular distance between centers of mass of CO2 and NO in the ground state is determined to be R = 3.703 A.