Reactions of Metal Carbonyls with Active Nitrogen

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Abstract
Ni(CO)4, Fe(CO)5, Cr(CO)6, W(CO)6, Mn2(CO)10, and Co(NO) (CO)3 were found to react very rapidly with active nitrogen, forming metal atoms. The reaction is accompanied by intense flames due to neutral metal atom emission spectra. The mechanism of the reaction is interpreted as a stepwise degradation: Me(CO)n+N→Me(CO)n−1+NCO. The excitation of emission spectra is shown to be most likely due to collisions of metal atoms (as they diffuse to the walls) with metastable A 3Σ nitrogen molecules. These are formed in the three‐body atomic recombination reaction and have only short lifetimes due to destruction on the walls of the tubular flow reactor. Quantitative intensity measurements of Fe(I) and Ni(I) flame spectra yielded rates of excitation of numerous levels of these atoms. The relative rates are found to depend only on the excitation energy, decreasing monotonously as the energy increases. Atomic mercury emission in active nitrogen was also observed and measured, as well as its quenching by ammonia. The dependence of the excitation rates on energy is experimentally the same for nickel, iron and mercury, except that the excitation of the 7s1S0 mercury state, which conflicts with the spin conservation rule if the nitrogen molecules undergo the A 3Σ→X 1Σ transition, occurs about 10−2 as frequently as the energy relationship would predict. It is inferred that this relationship is largely determined by the relative populations of the successive vibrational levels of the A 3Σ nitrogen molecules as these cascade down due to inelastic collisions from the highest levels resulting from the three‐body recombination processes.

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