3.2 Oxygen Addition
47
Fig. 3.7 a Measured effective bimolecular rate coefficients for the reactions of copper cluster
anions (circles), silver cluster anions (triangles), and gold cluster anions (squares) with oxygen as
buffer gas at a pressure of ~60 Pa. b A list showing the effective bimolecular rate coefficients for
Cu n
− , Ag n
− and Au n
− reacting with oxygen at ~60 Pa buffer gas pressure. K II , reaction rate. K c ,
collision rate. Reproduced from Ref. [29]. Copyright 1994 American Chemical Society
readily form a stable molecule CoO 2
− in reacting with oxygen. For cationic counterparts, successive oxidation reactions were found to virtually terminate when the
formed Co n O m
+ clusters displayed stoichiometric structures of (CoO) 4 (CoO 2 ) n
+ (n
= 0–3), or Co 2,3 O 4,5
+ . The loss of a Co atom in the reaction of Co clusters with
O 2 (usually termed as a switching reaction) was demonstrated to be consistent with
Stevenson’s rule [37–39] According to Stevenson’s rule, [38] the ionic products in
decomposition prefer to bear lower IP values, and the coordination of ligands can
reduce the IP of metal clusters [40]. Examination of the reaction rate constants for the
mass-selected cobalt clusters illustrated a strong correlation between the cluster sizes
and their reactivity, suggesting that the geometric structures and the release of stable
molecules could be a major factor in determining the cobalt cluster reactivity [37].
3.3 Superoxo and Peroxo States
Along with oxygen intake reactions for metal clusters, it is important to note that the
bonding mechanism between metal clusters and oxygen could involve charge transfer
with a concomitant activation of the O–O bond. The excitation of triplet dioxygen
(
3
g
− ) to the more reactive singlet state (a
1
g ) can be achieved by the interaction
47
Fig. 3.7 a Measured effective bimolecular rate coefficients for the reactions of copper cluster
anions (circles), silver cluster anions (triangles), and gold cluster anions (squares) with oxygen as
buffer gas at a pressure of ~60 Pa. b A list showing the effective bimolecular rate coefficients for
Cu n
− , Ag n
− and Au n
− reacting with oxygen at ~60 Pa buffer gas pressure. K II , reaction rate. K c ,
collision rate. Reproduced from Ref. [29]. Copyright 1994 American Chemical Society
readily form a stable molecule CoO 2
− in reacting with oxygen. For cationic counterparts, successive oxidation reactions were found to virtually terminate when the
formed Co n O m
+ clusters displayed stoichiometric structures of (CoO) 4 (CoO 2 ) n
+ (n
= 0–3), or Co 2,3 O 4,5
+ . The loss of a Co atom in the reaction of Co clusters with
O 2 (usually termed as a switching reaction) was demonstrated to be consistent with
Stevenson’s rule [37–39] According to Stevenson’s rule, [38] the ionic products in
decomposition prefer to bear lower IP values, and the coordination of ligands can
reduce the IP of metal clusters [40]. Examination of the reaction rate constants for the
mass-selected cobalt clusters illustrated a strong correlation between the cluster sizes
and their reactivity, suggesting that the geometric structures and the release of stable
molecules could be a major factor in determining the cobalt cluster reactivity [37].
3.3 Superoxo and Peroxo States
Along with oxygen intake reactions for metal clusters, it is important to note that the
bonding mechanism between metal clusters and oxygen could involve charge transfer
with a concomitant activation of the O–O bond. The excitation of triplet dioxygen
(
3
g
− ) to the more reactive singlet state (a
1
g ) can be achieved by the interaction