Negative ion mass spectra of some classes of metal carbonyl halides

The negative-ion mass spectra at 70 eV of the compounds Re(CO)₅X (X = Cl, Br, I), Mn(CO)₅X (Br, I), Re₂(CO)₈X₂ (X = Cl, Br, I), Mn₂(CO)₈Br₂ and Rh₂(CO)₄X₂ (X = Cl, Br, I) are reported. The negative molecular ions are absent and the current is mainly transported by fragments due to the loss of carbonyl groups. In the spectra of the bimetallic compounds a rather high intensity is displayed by ionic species containing the two halide substituents. The variations in the ionic abundances are related to the change of the metal-CO bond strength, while the nature of X seems to play a minor role.