Abstract The He (I) photoelectron spectrum of cyanoformyl fluoride NCCOF has been obtained. The individual ionization bands have been assigned by correlation with the known photoelectron spectroscopic data for structurally related species and by the use of semiempirical MNDO, AM1 MO and ab initio Green's function calculations. The cyano and fluoro groups were found to exert very strong inductive effects. Extensive delocalization of ...