Chemistry Reference
In-Depth Information
10
4
1.0
0.5
10
3
400 500 600 700 800
wavelength (nm)
10
2
200
300
400
500
600
700
800
900
wavelength (nm)
Figure 6.17.
Point-by-point absorption spectrum (O) of Mn(IV) in 10 M NaOH
obtained by pulse-radiolytic reduction of
MnO
3−
with
•
CO
2
radicals and
e
a
−
. Measure-
ments of absorption differences were made ≈5 µs after pulse. Inset: spectrum of MnO
2
in concentrated KOH (adapted from Rush and Bielski [183] with the permission of the
American Chemical Society).
TABLE 6.2. Rate Constants of Reactions of Radicals with
MnO
-
and
MnO
2
-
Radical
(/M/s)
(/M/s)
References
k
(
MnO
−
)
k
(
MnO
2−
)
2.6 × 10
10
2.0 × 10
10
[190-192]
e
a
−
O
−
-
8.0 × 10
8
[192]
9.50 × 10
5
a
1.8 × 10
3
a
[183]
•
−
O
2
6.90 × 10
9
a
8.1 × 10
8
a
[183]
•
−
CO
2
•
CH
2
O
−
-
1.9 × 10
9
b
[183]
CH
3
C
•
HO
−
3.30 × 10
9
c
1.8 × 10
9
b
[183]
CH
3
C
•
(O
−
)CH
3
7.20 × 10
9
b
2.0 × 10
9
b
[183]
•
CH
2
C(OH)(CH
3
)
2
1.85 × 10
9
d
3.3 × 10
8
b
[183]
a
1.0 M NaOH at 25°C.
b
The observed rate constants are at an average of ≥8 runs at 25°C in 0.1 M NaOH.
c
From Rush and Bielski [389] at pH 10.4 (alcohol radicals are in the protonated forms).
d
Premix pulse radiolysis at pH 9.4, 0.05 M Na
2
HPO
4
/borate buffer at 23 ± 1°C.
The reactions of formate and alcohol radicals were slightly lower than reac-
tions of
e
a
−
with Mn(VII) and Mn(VI) (Table 6.2).
The spectra of Mn(VI) obtained by the reduction of Mn(VII) by ethanol
radicals and
e
a
−
in the pH range from 4 to 9 are shown in Figure 6.18 [183].
The molar extinction coefficient as a function of pH at 610 nm is presented in
the inset of Figure 6.18:
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