Products of the gas‐phase reactions M+N2O and M+O3, where M=Na or K, have been investigated with UV photoelectron spectroscopy and bands have been assigned with the assistance of results from ab initio molecular orbital calculations. For the M+N2O reactions, the observed products were MO+N2. Measurement of the photoelectron bands associated with the metal monoxide MO allowed determination of the first adiabatic ionization energies of NaO and KO. The values obtained were AIE[NaO(X 2Π)]=(7.1±0.1) eV and AIE[KO(X 2Π)]=(6.9±0.1) eV. A similar study of the Li+N2O reaction gave AIE[LiO(X 2Π)]=(7.6±0.2) eV. The reactions M+O3, with M=Na or K, were observed to give MO+O2 as the major reaction products. However, for each reaction, a band was observed which was assigned to the first ionization energy of the secondary reaction product MO2. From the spectra obtained, the first adiabatic ionization energies of NaO2 and KO2 were measured as AIE[NaO2(X 2A2)]=(6.2±0.2) eV and AIE[KO2(X 2A2)]=(5.7±0.1) eV. For both the M+N2O and M+O3 reactions, production of MO A 2Σ+ was found to be favored relative to production of the MO X 2Π state, a result which has important implications in understanding the sodium night glow in the mesosphere.