Stimulated emission pumping spectroscopy of2Σ and2π vibronic levels in [Xtilde](v1v20)2π NCO

We report measurements of 2Σ symmetry rovibronic levels in the (υ 1, υ 2, υ 3)= (110)/(030) Fermi-resonant polyad and the 040 μ 2π states of NCO. The levels were detected by the technique of stimulated emission pumping spectroscopy in a supersonic free jet expansion following excitation of rotational lines in the Ã(100) 2Σ+−[Xtilde](000) 2π transition of the radical. Combining the new measurements and previously published data we have a complete set of experimental data for 2Σ and 2π vibronic levels of [Xtilde](v1v2 0) 2π NCO for v 1⪯2, v 2⪯4 and for the (010) 2Δ vibronic states. A fairly complete effective Hamiltonian is described and the parameters in it are fitted to a sample representative of all these data. We successfully fit the data to close to the experimental measurement accuracy and derive a unique set of harmonic and anharmonic vibrational terms. The results are interpreted in terms of the electronic structure and vibrational potential energy surface of the radical.