Kinetics of Co(a(4)F, b(4)F, a(2)F) and Ni(a(3)F, a(3)D, a(1)D) depletion by O-2, NO, and N2O

The kinetics of depletion of the first-row transition-metal atoms Co and Ni upon interactions with O-2, NO, and N2O were studied in a fast-flow reactor at a He pressure of 0.70 Torr. The depletion rate constants were determined for the first and second excited states of both atoms, Co(b(4)F(J), a(2)F(J)) and Ni(a(3)D(J), a(1)D(2)), as well as their ground states, Co(a(4)F(J)) and Ni(a(3)F(J)). For all oxidants, inefficient or no depletion was observed for the ground states of both atoms. Low-lying Ni(a(3)D(J)) also showed inefficient depletion, though this state has 3d(9)4s(1) configuration. The first and second excited states of Co(b(4)F(J), a(2)F(J)), which have the 3d(8)4s(1) configuration, were depleted very efficiently. The depletion of Ni(a(1)D(2)), the 3d(9)4s(1) configuration, depended on the oxidants; i.e., O-2 depleted this state by the gas kinetics rate constant, while the depletion by NO and N2O was about 1 order of magnitude slower. Efficient depletion of the atoms of 3d(n-1)4s(1) configuration by O-2 was interpreted by an attractive interaction correlated to a stable intermediate. The singly occupied antibonding pi* orbitals of O-2 are favorable to interact with singly occupied 3d orbitals of Co or Ni to form the intermediate. The depletion of the ground states of both atoms by NO indicated the occurrence of efficient termolecular processes at the low-pressure condition and implied the formation of a long-lived intermediate by the interaction between the 4s orbital and the singly occupied pi orbital.