Abstract
The photochemistry of the trioxalatocobaltate III complex was studied. It was shown that both the peak in the ultra-violet region (attributed to electron transfer) and that in the blue (attributed to
d->d
transitions) are photochemically active. Primary quantum efficiencies were found for various lines to be: 313 m
μ
, 0.365; 365 m
μ
, 0.345; 405 m
μ
, 0.085; 435 m
μ
, 0.06. The quantum efficiency of cobaltous ion formation is twice the primary quantum efficiency. No temperature dependence was detected. Ethyl alcohol (up to 75%) and acetone (up to 60%) did not effect the photochemical quantum yield. The radical C
2
O
4
-
is postulated as intermediate capable of reducing mercuric chloride in the course of the reaction. The reaction scheme consists of photo-excitation, primary dark back-reaction, dissociation of excited complex and non-rate-determining oxidation of the C
2
O
4
-
ion. The thermal reaction was also studied. It was found that the reaction rate could be presented by -d[Co
Ox
3-
3
]/d
t
=
k
1
[Co
Ox
3-
3
]+
k
2
[H
+
][Co
Ox
3-
3
]
k
1
and
k
2
were evaluated as 1.62 x 10
18
exp ( - 33 600/
RT
) s
-1
and 1.77 x 10
19
exp ( - 32500/
RT
) s
-1
(mol./l.)
-1
respectively. Both the neutral and acid reactions were, however, postulated to proceed through a pseudomonomolecular mechanism involving water molecules with the [H
+
] ion effecting the level of the transition state. Activation energies are discussed and finally the suitability of the trioxalatocobaltate III complex for chemical actionometry is analyzed.
Reference20 articles.
1. Bawn C. E. H. & W hite A. G. 1951 J . Chem. p. 339.
2. Bowen E. J. 1946 The chemical aspects of light 2nd ed. Oxford University Press.
3. J;Bowen E. J.;Soc. Dy. Col.,1949
4. Light absorption and photochemistry (including photo-polymerisation and the effects of light on dyes)
5. J ■Chem;Brealey G. J.;Phys.,1952
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