The decomposition of nickel carbonyl studied by flash photolysis

It is shown that the decomposition of metal carbonyl complexes can be studied by flash photolysis and kinetic spectroscopy. Ni(CO)$_4$ was decomposed under isothermal conditions by a high intensity flash of ultra-violet light; measurement of the amount of decomposition by plate photometry showed that at low conversion the rate of reaction depends on the square of the flash energy. This was interpreted by the mechanism $Ni(CO)_4+hv\rightarrow Ni(CO)_3+CO,\\ Ni(CO)_3+hv\rightarrow Ni(CO)_2+ CO,\\ 2Ni(CO)_2\rightarrow \text{solid products}.$ The decomposition is strongly inhibited by carbon monoxide, which reacts back with Ni(CO)$_2$ or Ni(CO)$_3$ and requires a third body. At high pressures, the mean collision efficiencies of the reactions $Ni(CO)_3+CO\rightarrow^MNi(CO)_4,\\ Ni(CO)_2+CO\rightarrow^MNi(CO)_3$ are about 3 x 10$^{-3}$; the mean lifetime of chemically activated Ni(CO)$_4$ is 7 x 10$^{-9}$ s. A new mechanism is proposed for the homogeneous thermal decomposition of Ni(CO)$_4$.