Chemistry Reference
In-Depth Information
10.0
8.0
6.0
4.0
2.0
300
400
500
600
700
Wavelength (nm)
Figure 5.18.
Transient absorption spectrum obtained for the
SO
−•
radical in N
2
-
saturated pH 7.4 water containing 5.0 mM phosphate buffer, 5.0 mM K
2
S
2
O
8
, and 0.50 M
tert
-butanol (adapted from Rickman and Mezyk [353] with the permission of
Elsevier).
the photolytic system of PS (Eq. 5.50) was described by mixed first- and
second-order kinetics [361]. The mechanism of the decay was given by Equa-
tions (5.53)-(5.55) [362]:
SO
•−
+
SO
•−
→
S O
2
−
(5.53)
4
4
2
8
SO
•−
+
H O
→
•
OH HSO
+
•−
(5.54)
4
2
4
SO
•−
+
S O
2
−
→
SO
2
−
+
S O
2
−
k
≤
10
4
/M/s
.
(5.55)
4
2
8
4
2
8
55
At 296 K, the rate constants of reactions (5.53) and (5.54) were determined
as 2
k
53
/ε = (2.5 ± 0.2) × 105 cm/s (ε is the absorption coefficient of SO4
•−
at
454 nm) and
k
54
[H
2
O] = 440 ± 50/second, respectively. Rate constants
k
53
and
k
54
were found to increase strongly and nonlinearly with increasing ionic
strength [361]. Reaction (5.52) was studied as a function of temperature (11.8-
74.4°C) and the rate constants were expressed by Equations (5.56) and (5.57)
[361]:
5
(5.56)
2
k
/
ε =
( .
4 8 2 0
±
. )
×
10
exp(
−
1 7 1 1
.
±
.
kJ/mol/RT cm/s
)
53
k
54
=
( .
4 7 0 1
±
. )
×
10
3
exp(
−
15 5 0 6
.
±
.
kJ/mol/RT /M/s
)
.
(5.57)
SO
3
with oxygen generates the peroxysulfate radical
(
SO
•−
) (Eq. 5.58) [352]:
The reaction of
•
−
•
−
•−
9
SO O
+ →
SO
k
=
2 1 10
.
×
/M/s
.
(5.58)
3
2
5
58
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