The He(I) photoelectron spectra of bicyclic N-chlorodiaziridines (exo- and endo-I; R1 = H, Me, COOMe, CF3, R2 = H; R1 = COOMe, R2 = Cl), N-chlorooxaziridines [II; R = Me, Me3C; RR = (CH2)5], and the corresponding N-H compds. have been recorded and analyzed using AM1 calcns. The N-chlorodiaziridines show exo-endo isomerism; however, only one endo isomer (R1 = CF3, R2 = H) is sufficiently stable for the measurement. The N-chlorooxaziridines are more stable than their N-H precursors. The compds. are characterized by three nonbonding orbitals n+NN, n-NN, and nCl (N-chlorodiaziridines); n-NO, nCl, and nO (N-chlorooxaziridines). These orbitals give rise to the first three ionization bands of the compds. The energy sepn. of the two nNN MOs of exo-I (De ~0.3 eV) is smaller than in the corresponding N-H compds. (De ~0.6 eV), while in endo-I (R1 = CF3, R2 = H) (De ~1.2 eV) it is larger than in the corresponding N-H compd.. In the oxaziridines, replacement of H by Cl leads to a small stabilization of the nO orbital. These findings can be interpreted by vicinal nX/s*N-Hal interactions (X = N or O).