Photoelectron spectra of isocyanic acid, isothiocyanic acid and hydrazoic acid excited by helium resonance radiation are presented. A complete identification of the orbitals from which electrons are ejected has been obtained by comparison with the photoelectron spectra of carbon dioxide, carbon oxysulphide and nitrous oxide, by consideration of the vibrational structure and intensities of the bands and by comparison with the photoelectron spectra of methyl isocyanate and methyl isothiocyanate. A clear relation is found between the photoelectron spectra and the bond angles in the neutral molecules.