New Rydberg-Rydberg transitions of 14N 16O have been observed by the technique of optical-optical double resonance multiphoton ionization (OODR-MPI). The analysis of S 2Σ+-A 2Σ+ (0,0), (1,1) and 4f-A 2Σ +(1,1) bands are reported. Molecular constants of the S 2Σ+ υ=0,1 levels are in good agreement with those derived from absorption data. The structure of the 4f(υ=1) level of the 14N 16O isotope can be fully investigated for the first time since the OODR-MPI spectrum is free from any overlap, in contrast to the corresponding absorption spectral region. No detectable spectral perturbation was observed for levels up to N=10, although the non-Rydberg G 2Σ-(υ=8) level lies at the same energy as the 4f(υ=1) level. The 4f(υ=1) rotational levels are described by an intermediate case (b)/case (d) coupling scheme and present a similar pattern to that of the 4f(υ=0) rotational levels previously studied from absorption data. Rotational constants B1=1.968 cm-1 and αe=0.020 cm-1 have been derived from our analysis and the B0 value already known from absorption work. The constant k, which is related to the quadrupole moment of the vibrating molecular core, has also been derived for the 4f(υ=1) level. Our observations suggest the presence of a "significant" amount of l=2 character in the lowest member of the ns series, (3sσ) A 2Σ+ state, and confirm the pure l=3 character of the 4f Rydberg level. © 1983 American Institute of Physics.